Slow Computer

I dunno what the fuck is wrong. I just formatted my computer, I have virus protection, my hardware is all decent, but for some reason my computer is running slow, and lagging, and all kinds of crap that's really bleaking me out.

UPDATE:
So I finally figured it out, I reformatted my computer and tried some stuff and it still wasn't working properly. I decided to switch my RAM around and see what happens, sure enough, I turn it back on and the screen isn't working. So I plugeed the screen into my onboard graphics card to see if that worked, it did AND my computer seemed to be running smoothly again, so I figured out it was probably my graphics card. So I opened up my pc again and started taking my graphics card out, when I noticed that one of the power cables wasn't in properly, so somehow my graphics card was still working and stuff but the power wasn't at full capacity or whatever, and I fixed, I'm awesome.