My computer restarts randomly and sometimes wont boot

[trademark2]

sorry if this is the wrong section i wasnt sure where to put it.

I took my computer halfway apart, cleaned the cpu fan, took out and replaced a CD drive(the same CD drive), and put it back together, and now my computer restarts randomly(within like 5 minutes ussually). one time when it restarted i caught a glimpse of a blue screen of death. before it restarted. sometimes, it wont even boot(hangs at various times). Sometimes if i can get it started up, it freezes up(mouse, keyboard, everything) (one time when this happened a small black rectangle appeared on the screen).

I know restarting randomly is supposed to be a power supply problem, but i didn't even mess with the power supply. Ive reseated the ram. I'm thinking it might be the motherboard, (perhaps from ESD)? although i don't think i would have caused it. I did leave the room briefly and my dog might have sniffed it(unlikely he would actually touch his nose to it though I would think). Or maybe its the fan. I should have held it still, but i just turned it the way it had least resistance. So, what do you guys think

I dont have a lot of test equipment, so I'd like to know the most likely thing I should buy.

 

[trademark2]

well this is odd... i took the cover off and now its working fine... so far... maybe a cable was touching a card or something hopefully

 

[loosley]

Check that all of the connections from the power supply to the motherboard, CPU, video card, and drives are all plugged in tight. Also check that the SATA cables to the drives are plugged in as well.

Finally, make sure the RAM is seated correctly. Maybe one of the sticks is partially unseated. You could also run MemTest86+ to verify the RAM.

 

[asantesoul]

make sure you mounted the motherboard correctly so the motherboard isn't shorting out..ensure ram is seated snug...ensure that all cords are connected correctly and are fit