Noticed the problem about 2 weeks ago, I think, and automatically linked it to a dips in the power supply, but when it started happening 2-3 times in a day then I realised it had to be an issue with the game, if you have any ideas as to what is causing it, PLEASE do tell.
It seems like it mainly happens when I am in singly player mode and using the track editor, e.g. today I put a couple of ramps on the blackwood rallycross course and then raced against A.I. on the course with the ramps placed. I then went back and viewed the replay and slowing the replay rate to 0.250x while the A.I. was going over the ramps, all of a sudden the computer momentarily(split seconds) goes off and then switches back on/restarts.

Hope this helps

You are blue screening by the sounds of it. C:\windows\minidump should have the latest dump file when Windows crashes. I can take a look at it for you or you can take a look at it yourself.

try this.

I had the same thing last year and it turned out that the cause was overheating because the fan stopped working.

thanx guys for the suggestions, I will have a lookie