I have built 4 machines, and upgraded 3 of them at least 3 times.
All have worked fine apart from one, dunno that PC even when it was manufacturer made never ran nicely I think that the spot the case sat was cursed or something.
Basic tips, read the mobo manual for connector orientation
and always check everything twice before even plugging in the power cable.
Thermal paste (Arctic Silver III is a god send)
A CPU running at 70-80C will crash fairly easily when you try to install an OS (trust me I know)
Also dropping a computer is not recommended, though I have dropped one of mine and it has never been the same since, I now use it as a server it is so stable. (I dont think that an improvement in Stablility is the most common result of dropping)
XP Abuser, how the fk did you manage to FLASH your BIOS in windows, they all say they cannot run except in PureDOS