Now, I'm not claiming to be perfect, or that mistakes don't happen, but I really must just complain a little bit about some people who take money from people to build computers when they don't actually know what their doing.
Somebody in the family got me to take a look at their computer to speed it up a bit. It was a 2.8gig P4 w/ HT on a P4P800 and wasn't getting the benchmark scores it should have been. The guy who'd built it was a guy the owner knew from work.
Anyway, first up was the fact that the graphics drivers were crap - old ones probably grabbed from windows update, which we all (should) know are outdated and rubbish - sorted that and some other drivers.
Next up, the hard drive was set as Primary Slave with NO other device on the channel. Modern motherboards will let you do that, but technically it is not possible. Anyway he'd set it on cable select and plugged it into the wrong connector, so I jumpered it to master and put it on the right connector.
The final problem was a real treat - this guys 2x 512MB sticks of 400mhz DDR RAM were in the WRONG SLOTS! So no dual channel! I sorted that out and suprise suprise everything worked as it should.
Still, at least he managed to plug the 4-pin +12V cable in