The only time that I have seen this is when a cpu overheats. If your not overclocking you might want to check the fan on your processor to see if its running properly.
I am running WinXP. I have 1 gig of memory. I have 3 GHZ of processing power. Lately the computer has been restarting on its own accord. It tells me that windows has shut down to prevent damage to my computer. Followed by "IRGL_NOT_LESS_OR_EQUAL". Then I am told to check my computer for new programs or hardware. The tech information that it gives is the word STOP followed by a bunch of zero's with a few letters and other numbers thrown in. It then tells me that it is beginning a dump of my physical memory. Does anyone have any ideas as to what I need to fix or replace?