It was definitely the cord. I checked it with another computer. No power issues since then.
Unfortunately, now I have a slightly worse problem. CPU runs hot (50C idle and 70-80C when gaming), take it out, remove old (slightly burnt) thermal paste, reapply thermal paste, put it back in, clamp it down, reattach heat sink/fan, recable and boot up. Everything's fine (fans spin and everything) except no beeps and no post. :(
Possible problems:
CPU might have not been seated 100% correctly. It might have shifted a bit while I was putting the heat sink on. I'm going to take the heatsink out again and check, but it's a major pain putting the heatsink back on (
the restraining clamp doesn't have a whole lot of give and it really take a lot of force to get it to catch)
A bent CPU pin. Bent it back into place but not sure if it stayed that way after I put the CPU back in.
P.S. - Please bear in mind that I'm still very green when it comes to the insides of computers. This past few months have been my first couple of times opening up a computer and trying to install/repair components. I'm admittedly not very skilled at it, but I'm a
quick normal okay learner and this is a fairly old system, so it's no biggie to replace a component if that's what I have to do. It's just frustrating not knowing what exactly is wrong.