Ahh, you have just got bitten by the dreaded nvlddmkm error otherwise known as a TDR. I as well as many other ppl have been experiencing this nightmare. The short and sweet is a TDR can be caused by many different issues. However, the same symptom appears. The screen freezes and goes black, comes back on with the display driver stopped responding message. This problem can be because of bad drivers, dodgy hardware, vista/nvidia conflicts, heat... etc. I have been beating my head against a wall for 4 months now with this on a brand new Dell XPS 720.
The bad news is, there is no magic bullet to fix this problem. You need to figure what is causing the problem which usually involves a whole lot of trial and error since no solutions works for everyone. In my case, after trying many other fixes with no luck I finally did a clean instal of vista. I got the error after the first boot. The MS hotfixes that are supposed to fix this have not worked for me but have for others. If you go to the Nvidia driver page there is a link to get said hotfixes. Maybe they will work for you.
At this point Im at a loss as to what to do next other than demand Dell send me a computer that works. This problem, for me is not confined to SH4. It happens randomly in any setting and even when my comp is sitting idle.
I have tried the MS hotfixes, multiple drivers, tweeks, twitches and even a voodoo ritual to no avail finally ending with the vista re-install. Its not heat either as my cards run at 55c idle and this problem happens at idle too.
This thing is like a vampire in a bad B movie. It just keeps comming back.
Oh, try googling nvlddmkm. There are many topics out there on it. Maybe one might solve your issue. Good luck and Cheers!