|Also, is your computer relatively new or old? Have you done any upgrades? |
If new, maybe a mfg issue (like a poorly mounted cpu heatsink) and maybe under warrantee.
If old, maybe dust (as above) or maybe other issues.
if recently added a large video card, you may need additional cooling in your case - try adding another fan and/or moving PCI cards around so there is space around your video card.
Make sure there is room around your hard drive(s) (try moving to a more open bay)
Try downloading a program like SpeedFan which will give you specific temperatures of CPU, Graphics, etc for more clues.