Do you hear any beeps?
Looks like its freezing at startup, on the initial 'splash' screen with video corruption. So possibly motherboard/video hardware problem, definite basic hardware issue. If you can put a video card in there that would be worth a shot.
Since you had it in storage it is also worth tightening all your connections, re-seating the RAM chip(s) and cards etc.
i feel dumb, the power cord wasn't plugged in all the way...
Ah. Don't usually see 'partial power' as an issue! Usually either on or off, LOL. But my last edit did say to tighten all connections so I got it in a way.
Sorry guys, this problem popped up again after a few months, i didn't do anything but restart it when it appeared again.
What i have tried:
A different monitor
using different power sources (directly into the wall, no power-strips)
Opening it up to see if there is anything wrong going on inside, but not that i can see.