My computer turns off during burning onto a dvd-r!!! Why??

[amonales]

I have an external dvd-rw LiteOn recorder and a Nec Versa Laptop. I ripped a dvd using dvd decrypter and burned it with dvd shrink. It hasn't been a problem so far but this time during burning onto a dvd-r computer turned off. I tried with another dvd and the same thing happened only when i was starting to burn. Than I went decoding DVD MPeg-2 movie into a XviD format and in the middle of decoding the same thing happened-my computer turned off.
Does anyone have an idea why this is happening? Let me point out that otherwise my computer runs for hours and doesn't turn of by itself.

Thx

[setarip]

If you're running under Windows XP, perform a "System Restore" back to the last time things were running properly. If that doesn't resolve your problem start checking your hardware (Is your video card seated and connected securely?)