I think the last time I cracked open some compu-tower ribs was at the yarn shop back in 2009. We had these three mildly crappy Dell P4 towers for running the POS system and everything, but they were acting like they were the ultra crappy kind. Just slow as hell and unresponsive and bullshit. Stev and Hannah were all angsting about whether we could afford new ones and how to go about getting them, and I was like, "lemme take a look." Reader, these 3Ghz machines were choking along on a half-gig of RAM each. I got on Newegg, and was like "Gimme the credit card, I'll get you some rejuvenated computers for like $140."
Once the sticks arrived, I got the backroom and cafe computers beefed up and breathing easy in like 20 minutes. Then I upgraded the main counter PC, tried to power it back up, and got nuthin'. I cracked it open again to make sure I hadn't left anything loose, and we were all like "Uh, was that creepy amber light there the last time?" It was totally not.
I searched the internet for the manual again, and it turned out the amber light on the mobo meant "power fault," usually a bunk power supply. So I grabbed a screwdriver and tore the fucker out, tossed it in my backpack, got on my motorbike, and jetted up Milwaukie to Free Geek, where they confirmed it was toast and sold me a better one (for the $15 I had liberated from the petty cash drawer). Which totally solved the problem, and left me feeling like quite the techno-samurai moto-badass.
And then the whole shop folded explosively in August and we were all out of work, but at least the computers were non-bullshit for as long as the shop survived.