Solved Which graphics card should I buy?

I'm talking very, very, very low-end. I have a 240 watt power supply on my computer, and I can't replace it or get a new one. I can't. As in, I can't, please don't reply if you're just going to tell me to get a new computer. I tried looking up online for video cards that will work on my computer, but everyone suggests these video cards that have a minimum required power of 300 watts. They say it's okay because the card itself doesn't take 300 watts, but I've already tried this with the Radeon HD 6450, and it did not run on my computer at all (which is an HP Compaq Elite 8100 Small Form Factor. Running Windows 7 home premium.)
Are there any graphics cards out there that I can get for my computer? I really just want to play low-end games like TF2.

I can't find anything that will run on my 240 watt psu.
Is it possible to upgrade my PSU? I imagine it would be hard, since my computer is a low-profile small form factor

I think I'll just save up money to get a better computer, but thank you everyone for your help.