(adsbygoogle = window.adsbygoogle || []).push({}); So i recently bought a PSU for my new graphics card. i hooked it up everything worked fine for a couple of days then my PC would turn on but my screen keyboard and mouse wouldn't work at all. i tried unplugging it and plugging it back in but that didnt work. i also tried removing the RAM but still nothing. and im sure the graphics card works because the fan is turning on it.

Possibly damaged RAM (from when you opened up your pc) Try only one stick at a time in all the slots if this doesnt work try the other stick(s)
check if you need a 6pin connector plugged into your graphics card
try removing all peripherals and then boot
test the PSU (kits are only about £5 ($10)
try reseating everything (cpu, gpu, RAM) etc.
had the same problem myself a while back turned out to be faulty ram