My PC restarts when watching dvds and gaming

[IHATEDLINK]

My PC restarts when watching dvds and gaming :S!!
I goes OK for like half an hour but then it just restarts!
And this doesn't only apply to dvds and gaming, I can't even mess around with Google Earth!
I know this isn't just an Ubuntu problem cause it also restarts when I'm in Windows. So I'm guessing hardware.
Is my fan not cooling enough or something? Cuase it used to make A LOT of noise and I reduced the speed a little, i don't remember how much, i don't even remember the original settings! it was a long time ago.. :S
Here are some of my specs:
Intel Pentium 4
512 of RAM
nVidia GeForce4 440 MX

Please help!

[IHATEDLINK]

COME ON!!! Please i need some help.

[tamoneya]

my guess is it is over heating so you should try to improve cooling or decrease the system load. To confirm this try to get some temp readings with lmsensors as well as some readings from top.

Please dont bump a post for 24 hours.