PMG5 quad, runs perfect, then randomly overheats and crashes

i have little experience with mac computers. i have a PMG5 quad, i think is overheating. system boots fine, idles fine, however, soon after an application is launched the fans on the system kick to full power then screen darkens along with a message saying i need to restart my system. then the computer freezes completely.
i was thinking possibly the cooling system coolant is low. i did not see any signs of leaking however i did notice rather hot air coming from the back of the unit. i was reading up on this and apparently the G5's s sometimes have this problem.

if this is a redundant post i apologize.

thanks for any help

Dragon,

I would suggest running some maintenance checks to see if anything is wrong with your PMG5. You can use Disk Utility in the Mac itself, but it's probably best instead if you pop in the original installation disks and boot from the disk. Once it's booted, then you can run Disk Utility using the original installation disk. Verify the disk and see if there are any problems.

Another option is to install SMARTReporter and see if it detects any problems with your drive.

If those tests pass, I'd move forward to other utilities, such as MainMenu, Cocktail,
MacJanitor or OnyX. The overheating can be signs of serious problems.

Egidio,
thank you for your advice. the Disk Utility solved some problems in the Extensis folder i think it was?.. as for the overheating, i ran some programs and could not get the problem to repeat after the fix. thx again.