My very first build was my parents' system which was just replaced last month. Athlon XP 1800+, 256MB PC2100, 80GB Maxtor hard drive, I talked them into a Geforce3 Ti200 instead of integrated, since I was into games. It was a killer upgrade from their previous rig, which my dad built - a Cyrix 6x86MX PR200 150MHz w/64MB and a SiS 6326 4MB. I assembled their entire XP1800 rig without a hitch, hit the power switch, and the fans spun, but nothing else - no beep. Great. I got real upset (I was only 14 at the time) and so I unplugged all the cables and plugged them all back in, then started her up perfectly. Must have been a tiny bit of corrosion on one of the connections.
I built a system for myself later on, my second build - an Athlon XP 2400+ with 512MB PC3200 and a Radeon 9600. This one started up the first time, and had no problems until a driver problem... I turned both displays off somehow in the ATi control panel and had to wind up reinstalling Windows XP cuz I had no knowledge of booting in VGA mode >_<
My third build was for a friend, he wanted something for music, so I was building him a P4 3.2 on LGA775 with 512MB PC2-4200 and a 160GB hard drive, using integrated graphics and a Sound Blaster Audigy. I ordered him the wrong motherboard - I was trying to get him DDR2, but ordered him a DDR-based motherboard. 🙂 Instead of RMA'ing and losing 15%, I turned this into my next build, and ordered him the correct motherboard.
My rig based on that motherboard was a P4 3.0GHz, two 512MB sticks of Corsair ValueSelect PC3200, and a Geforce 6600GT for PCI Express from Leadtek. Two months after building it, the video card crapped out on me. I didn't know what the problem was, because it was so intermittent. Integrated graphics ran fine, then the 6600GT graphics card would run once every four boots or so. I was angered, and sold off all the parts except the video card, RMA'ing it for a replacement (which I then sold) and I, at the time, blamed the whole thing on PCI Express not being perfected yet (it was a new technology at the time).
So I pieced something together off a forum, my best build so far. P4 2.8 Prescott, same two 512MB sticks of Corsair, and originally a Radeon 9700 Pro. I wasn't getting high enough framerates in my favorite game of the time, which was Need for Speed Underground 2, so I got an XFX Geforce 6800GT for AGP. It clocked higher than 425MHz on the core, but I never really used it much over 410MHz, since the CPU was more of a bottleneck. I got a Zalman CNPS7000-Cu, and this started my love of Zalman heatsinks. I clocked my Prescott to a 250FSB, and it ran at 45C under load at 3.5GHz. I'm 100% serious. This was in an Antec SLK3700-BQE case, with an MSI 875P Neo-LSR. I ran that rig until I sold it to buy a car. What's kinda funny about this rig, at the time I was in a business class at school and for a project, I had my friend take a video recording of me talking about computers as a business person, then building my P4 2.8 rig. It's funny, because like so many others at the time, I didn't know how much AS5 was a proper amount. I put too much on, it oozed off the sides of the CPU, but luckily didn't reach any contacts - just did enough damage to not allow it to boot that time. Undid everything, realized there was too much AS5, cleaned it all up and reapplied a smaller amount... and clocked her back to 3.5GHz. :-D
One of the greatest flub-ups in my history is not one that I did. It was one that one of my friends did while I was with him at school. You guys were talking about overclocking school computers. Well we had an A+ Hardware class, and I was trying to milk more performance out of our slow Celeron D's running 2.53GHz. I got mine running at over 3GHz by clocking the memory down to PC2100 (we were supplied with PC2700) and increasing hte bus speed. Maximum speed I got to was 165FSB, resulting in 3.14GHz (yes, Pi GHz) and so my friend John tried the same. I tested mine Prime95 stable for a weekend, then recommended he try playing around with the bus speed. He didn't exercise caution - and jumped straight up to 165FSB, frying his chip. 😛
I received an XP1700 rig from a friend of mine who I built a 3.06GHz P4 Northwood rig for as a replacement, I wanted to test his "old" XP1700 out, and so I took the heatsink off to look at his chip and get the spec markings. When I put it back on, I secured one clip, then the other - but the first clip came undone in the process. This is the only time I've ever smelled fried processor. There was a burn mark on the underneath side of his processor. I saw the smoke - just a little bit. I didn't like myself after that. haha