Hi guys, opened up my PC a couple days ago to measure the insides for a new GPU, which necessitated removing the PSU and current GPU. Ever since I put it back together it has two problems:

1) About ten seconds after I turn it on, it turns itself off and then back on again. The PSU appears to be plugged in correctly and there are no loose cables hanging off it.
2) None of my video outputs work. DVI, VGA and HDMI on both the processor and my GPU show up as 'no signal' on my monitor (which is definitely not broken as it still works with my other devices).

I got this thing back in 2013. I picked the parts but didn't put it together myself, and I'd rather not pay for repairs that I could do myself. Roommate says all the internals look fine and are plugged in correctly. Aside from the weird restart when I turn it on, it seems to run and sound fine.

If anyone can help I'm stumped and I really need this to be fixed pronto since my laptop is ass, even for uni work and web browsing.

Pic is of my PC's internals and back. 1/3