IMO, overheating is the greatest enemy of any computer system...that's why there are fans in the PSU, coolers for hard drives, heatsink/fan for the CPU, coolers for some video cards, case fans, upper temperature limits for CPU operation, etc.
Computers, like humans, just don't function well when an excessive amount of heat exists on/around components.
I would do my best to eliminate that from the list of possible factors affecting my system.
Cases, How to Avoid Overheating - http://www.hardwaresecrets.com/article/142
Cleaning the Interior of your PC - http://www.bleepingcomputer.com/tutorials/cleaning-the-inside-of-your-pc/
Computer Cleaning Information - http://www.computerhope.com/cleaning.htm
The worst part about overheating, IMO, is the fact that there are insufficient mechanisms to warn the user that such has occurred...and users often ignore typical signs that may signal such. No error messages are generated reflecting overheating by Windows...probably because the O/S is not capable of detecting any evidence of such until failure occurs in some part of the O/S.