Building a PC is like putting LEGO bricks together. Each piece fits on the next. The HARD part is tuning your PC to optimal settings. Heat, Power consumption, cooling, fan speeds, hardware burnin, etc are the more difficult parts. These are time consuming. Anytime I build a PC for a friend or my family, I always do a very difficult burnin test. THis goes as follows:
Derive 1,800,000,000 digits of pi.
Derive 1,950,000,000 digits of the mathematical variable e.
Run AquaMark 10X.
BurnIn Test 4.0 5X.
PerformanceTest V5.0.
The two derivations are run at the same time. The other tests directly after. I have the derivation tests loop for 36+ hours. If the PC doesn't stand up, then it doesn't survive me (I trash it and rebuild it, possibly with new parts.) This is very EXTREME, and most people don't do this kinda thing. Running a PC at full for 36+ hours is very hard on it, so don't try this unless you are willing to spend extra to replace the parts.
BTW- I CHARGE $300 for the Burnin tests I run, because that covers at least a portion of the replacement parts. If a PC passes these tests, then it will pass any other test you can throw at it.