The first thing that happened was, sometime shortly after building my PC, I wrecked the processor. A brand new AMD Phenom II 3.0ghz X4 black edition. Whoops!
Now, what happened was, I was attempting to replace the default heat sink. I failed to realize that thermal paste holds like hell if it's not heated. I attempted to pull the heat sink off of the processor and ... pulled the processor out of the motherboard right along with it. I looked at the bottom... bent pins. Son of a bitch.
I was too pissed off to think to attempt to straighten them, that was quite a costly mistake. I learned after that to heat the paste, such as running CPU intensive applications like folding@home for a little bit and THEN pull the heatsink off with a slight back-forth twisting motion.
The second blooper is a funnier story. One night my PC shut down and I heard a sudden, loud, non-stop "BEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEP".
Uh oh... that can't be good. I tried to start the pc back up... no deal. Oh crap. I simply couldn't figure out the issue although I suspected the motherboard had gone bad. I tore the pc down piece by piece. Even after disconnecting the motherboard from the power supply I still heard the beep. "It is the UNDEAD!" I thought, or some such. Why would it still be beeping after disconnecting the power from the motherboard? Well, some internal battery, I presumed.
After removing the motherboard from my room here I still heard the beep... coming from inside the room. Oh shit... it's not the computer! Come to find out, it was the UPS! It must have gone bad, or at least partially. That explained why the PC shut down but a couple other things that were still plugged into it were still going.
Bad UPS? Fuck it, my PC was alright! Woo! I tossed the UPS out, put my pc back together and all was right with the world again.
Definitely some funny stuff there, but I learned from my experiences and am smarter now for it. I learned more about PC building... the hard way... and am currently almost finished building my sister a PC. It's going much better @_@;