And don't forget the thermal paste! myrialux once built me a computer and it turned out that the part that needed to be stuck to the motherboard with thermal paste (the processor?) was a return--we didn't notice it at the time--and didn't contain the thermal paste packet, so he forgot that the concept existed. The resulting computer would overheat and randomly shut down, and when I complied at length and very loudly, myrialux drove back across the state the next weekend (we were in an LDR at the time) to take a look, realized what the problem was, and spent some time swearing before I demanded to know what was going on. XD The motherboard had warped.

The other symptom the computer was exhibiting was that I'd touch a metal part on the case, it would spark, and the computer would shut off. We were never sure why that happened (IIRC), but fixing the thermal paste thing fixed that too.

I had that computer for the better part of a decade until I accidentally installed malware--a banner that looked exactly like the Adobe Acrobat update notification banner, arg--and in the process of trying to clean it out, myrialux decided he was tired of having to support the frankenstein and used part of his yearly bonus to buy himself out of the service contract by getting me a Mac. :D