Thanks for the additional information
Suggest that you ask around to see if you can borrow a
PS/2 type keyboard this ib case the USB ports are either broken or disabled.
Going offline soon so will leave you with the below which will take you until tomorrow to sort;
The following checks require the computer case to be opened so take the following safety precautions 1st, disconnect the power cord from the wall socket, press the case power button for twenty seconds or so to get rid of any residual charge in the system, take anti static precautions before touching anything inside, you can do this by touching a bare metal part of the case or PSU;
Remove the CMOS battery and leave it out overnight.
Remove the RAM and leave it out overnight.
Tomorrow, put one stick of RAM in the slot nearest to the CPU.
Reseat the GPU.
Check all internal connections are secure,
Put the CMOS battery back in.
Connect the screen to the GPU.
Connect the keyboard,
Connect the power cord.
Power up the PC while crossing your fingers.
Post back with an update when you are ready.
You are welcome btw