New to home repairs

As title suggests im new at this, so plese go eesy on me.
I have a laptop i am trying to replace the screen on: Compaq Presario C700 (fixing old laptops as a learning/exp tool)
I ordered a 'new' used screen which i replaced the old one with, this is where the problem begins.
I put on the new screen, and the computer wouldnt even turn on. power light would activate for, like, half a second then nothing. So i put the old screen back on which at that stage the computer itself worked (turned on-but screen horribly damaged).
So i presumed the 'new' screen was defective, and decided to try and get the new screen active by using the old screens parts: ?alternator/adaptor bar? for the LED backlight (my terminology may be incorrect here), and the 30?/40? pin cable that connects to the back of the LCD screen.
Bad move.
Now the old cracked screen that at least the computer powered on with, no longer powers on.
So, a few questions for those that are far more adept at PC repair than some dumb noob.

Can what i have done by switching out components cause more damage to the other once working components, if those components were shorted and respectively cause further shorting? (i dont even know if that makes sense or is a thing, forgive me)

What would cause a screen to prevent the laptop from powering on?

Can anyone provide some recommendations/information to help locate with precision the fault?

Is there any other questions i should be asking that im not?

I have switched out the screens about 3 times each now, with 2 of those times being carefully inspecting the cables are mounted correctly (to which, there may be something simple a noob is missing)
I wish to avoid paying for someone to rectify this for me, as I wish to rectify it myself and learn valuable in the process.
I would greatly appreciate any input from more experienced users, but go easy on the jargon, im new at this.

Thankyou veeg for your response, it was in fact videos like the one you posted that inspired me to try a screen replacement. I must have viewed at least 8 different ones like it. Alas, it does not really help that much at all. Actually replacing the screen is not the issue, i have done that upwards of six times now, my issues are getting the screen working. I have detailed the issues to the best of my ability in OP.
Thankyou again for your input.

PeterOz said:

Were they the exact same screen.
A lot of laptops have same model numbers but different screens - not swap-able
They must be like for like.

Click to expand...

This is a great question, to which i cannot answer in great detail. The screen i bought sported the same model numbers on the top right corner of the plastic casing: C700. It in fact looked identical, Is it possible they were not?
Thankyou very much for you response/question in helping me locate the issue.

Bruce said:

While I have to take my hat off to you for even attempting this task, I have to also say, you need to know when you are out of your league.
Yes, it's the best way to learn, to dive in and get your hands dirty, but having pulled many laptops apart, I know all too well how simply they can break.
From the flimsy plastic molding to those **** ribbon strips and their little docking clips.

My first guess is the 'new' screen was either also damaged, or not compatible.

Click to expand...

Hi Bruce, thanks for the response.
Your assertion may be correct, and the task may have been beyond me. But I would also contend that doesnt explain how I could put the old screen back on at least twice before it all went pear shaped. The best form of learning is having a go, right?
To the best of my knowledge no ribbons or docking clips are/were broken (from a visually observable perspective, anyway).

Can these ribbons and docking clips break without being visually observable, and how fragile are these things?

Is it possible that a screen off the exact same model Presario C700 assembly was not compatible?

The 'new' screen may also have been damaged as you postulated, could utilising damaged parts from that screen on the old cracked screen have caused further issues with the pre-working (albeit damaged/cracked) screen, further causing it to not work after a third switch around?
Answers to these questions would be very much appreciated.

PeterOz said:

Were they the exact same screen.
A lot of laptops have same model numbers but different screens - not swap-able
They must be like for like.

Click to expand...

Are there any numbers/identifying indicators on the back of the screen you can recommend checking, and i may be able to give you (and myself) a proper answer to this line of questioning?

Thankyou all so much for your answers @Bruce and @PeterOz. Very informative both of you.
I will look into what both of you have said further and respond. From memory, some numbers may have been different by one value.
These answers are incredibly informative, and give me plenty to think about and inspect. I will definitely keep you both posted as you have been more than accommodating of my requests, I will probably ask for some advice on purchasing YET ANOTHER screen and maybe some ribbons and such.

The purchase was not from a 'reputable' dealer per se, it was from an ebay seller, and the screen i purchased was the whole screen assembly including the front and back case and brackets, ribbons, cables, adapter bar: sold as the 'screen assembly'.

I am going to sleep. I will get started on answering your questions in more detail in the next few hours/tomorrow (depending on your time zone).
Again, thankyou both very much for the intuitive and timely responses. I believe they may serve as very good guides to get me going in the right direction.
I think (if i knew about) 'Rule 2)' would have been very beneficial in my circumstances, it is a shame i wasnt aware of/practiced it. I was in doubt and did just about everything and anything.

I look forward to responding to you both in detail in the very near future.
Thankyou both so much.

I am one of those fools that learns from mistakes.

PeterOz said:

It all depends on
1) Is the supplier reputable and puts that info on.
2) Is the screen brand new (yours is not) or has the sticker fallen off as the glue is weakened by the heat.
3) Is the new screen any good - even a brand new screen can be DOA

Even if the parts look the same it does not mean the same.
Something as simple as a cable can look the same but unless you know the part number is exactly the same.
No revision numbers then the cable can be terminated differently, you then have to bell out the connectors.

Many Many parts look the same it is only when you start to read the id names/numbers that you can be sure they are the same.

Yes

You either need experience - not you (Please do not take this comment the wrong way we all had to learn)
OR
a service manual to show what outputs you should be getting from each component.

Click to expand...

Exhibit 'i)' images attached will be the cracked original screen that i needed to replace; and exhibit 'ii)' is the replacement purchased from ebay. I know it may be time consuming, but if you can understand those numbers i'd really appreciate a dumb-dumb break down of what they mean. If you can, i realise that may be time consuming and tedious. ( i hope the file types work for you, i had to resize, im still lurning. If not im happy to resupply)

1) The supplier did not include the info you showed in the screenshot you provided above. I did find similar specifications as to what you provided, but as an inexperienced 'technician' i just assumed C700=C700, it appears this is not the case.
2) The replacement screen was labelled as 'pulled from working computer; no faults' I am highly dubious at this item description. Then again, maybe it was all my fault putting on parts that shouldnt go.
3) I am not 100% certain, is there some kind of test i can do to be certain? I only have the c700 laptop to test this so unless there is another method, i dont believe i could test it. But please, if there is another method, i would appreciate to hear it.

I assume there is enough discrepancy between those numbers to be incorrect and 'terminate differently' compounding further problem. If it is not too much trouble, could you briefly explain this 'bell out' of the connectors?
I would greatly appreciate your experienced input on the numbers i have provided.

YES, no offense taken, i definitely need experience, but i think i covered that a couple of times in the original post.
And i would very much appreciate to know more about these service manuals, is there a website with, like, a library of service manuals?

Thankyou so much again for your input and participation here sir, greatly, greatly appreciated.

Bruce said:

When you say you got a 'new' screen, do you mean the LCD panel that goes into the hinged screen top of a laptop, or the whole hinged part itself - complete with all the LCD stuff inside the outer casing?

But to answer your questions...
a) 100% it's a great way to learn, only surpassed by someone teaching you first
b) if you are replacing the LCD panel and backlight components that then go into the outer shell casing then yes, many things can go pear shaped
c) laptop manufactures change their models very regularly, so while getting the same screen for your model should be a good indicator, it is no guarantee. For example, were they the same motherboards?
d) as to utilising bad parts, it all depends on what the damage was. If there was a shorted circuit, or a faulty power flow issue, then that would have effected the target component as well

Click to expand...

Hi Bruce, The whole hinged part complete with the LCD and components inside the case and the case as well.
a) That is why i am here pestering the masters (you)
b) to begin with, this was not my plan, but upon finding a whole 'screen assembly' i figured the lazy way out would be to switch that whole piece over. It was only after i failed that, that i started switching up LCD screens and backlight adapter bars.
c) This is a very relevant question to which i have no idea, and i am not sure i could easily get an answer to that, as i have no idea where the screen originally came from/off, except for the fact that it had the 'C700' logo imprinted in the case exactly like the one i already did. I assume by your question that this is a very important factor to screen replacement? Or just replacing parts in general? yes?
d) I am thinkng that this may be my issue, i could be wrong and maybe it was my inexperience and purchase that was the issue. I presume i may be able to provide a more precise retort to this in the future after you blokes answer a couple more of mine and fill in some more blanks. ( as if i did make bad purchase, then it was my fault, and likely not a faulty component... i presume)

Thankyou very much for your input and participation Bruce, i greatly appreciate it.
I feel like i am getting some solid answers, even if they obviate my ineptitude and inexperience.

Thankyou everyone for your participations. I feel like i am on the precipice of some valuable learnings here, which may be very useful in the future, as i wish to work my way up to tinkering on an old gaming pc i have, that i power surged, but it still sort of works, but id like to refurb to make it actually work how it should/used to pre power surge.