So I finally ordered a new PSU to replace what I assumed was a faulty one. Got it in, flip the switch, the power LED on the front of the case just steadily blinks. Motherboard is an AsRock A320M-DGS, but I can't find anything in its manual about this blinking, other than something about sleep mode, which definitely isn't the case here. Anyone know what's going on?

UPDATE
Well after unplugging and replugging in some stuff, now, I don't even get the power light. I suppose this means it was the motherboard all along, huh?

UPDATE 2.0
Well now we're back to the power LED blinking. So that's a start.

What were the symptoms that made you suspect the PSU in the first place?

https://www.gog.com/forum/general/computer_completely_crashes_trying_to_play_any_game_now_seems_bricked

It might well be the mobo, but a lot of things might affect that too. Bad peripherals may make it appear to be the mobo. I would start by disconnecting as many peripherals as possible first. If you have a dedicated graphics card, remove it and try the integrated graphics. Disconnect any peripherals you can get away with. Pretty much HDD, monitor, KB to start. If you have multiple pairs of RAM, start with one pair. If it starts up, then try reconnecting the rest one-by-one.

Also make sure anything connected is seated properly. Every stick of RAM, If your CPU heatsink clips on, make sure its clipped all the way on (had a friend once whose computer wouldn't boot, and clicking it in place fixed it).

EDIT: Nevermind, MB dependant.

Did you check the manual about the blinking pattern? Dunno if all MBs do that but mine blinks a certain number of times to indicate what component is giving an error?

Talked with a friend. The good news is my birthday is coming up, which means I'll have some money to spend. We'll take out and test the graphics card, optical drive, and hard drive. If they're fine, I'll spend ~$250 or so to get new a new mobo, a better processor, and some new RAM.