Whenever I am running an application that is heavy on graphics and/or CPU usage (like a video game or a video editing/encoding program) I will sometimes get a random BSOD. The frequency that this happens is increased if I have more than 1 instance of the application open at once (if more system resources are being used, it is more likely to happen) This has been going on for about a year now. I have run Microsoft's RAM checking tool to see if the memory was at fault, but it did not report any errors.
This is on a Dell XPS420 with Q6600 CPU and 4GB of PC2-6400 RAM
I have had 2 different operating systems on this PC. First was Vista home premium 32bit, the second was 7 ultimate 64bit. I have had 2 different main drives, first the stock 500GB HDD, then switched out to an 80GB SSD. And two different graphics cards, a 512MB ATI radeon 4870, then a 1GB ATI radeon 5870. This problem has occurring throughout all of the changing/replacing of components.
I asked around and one or two people have suggested it is an issue with the CPU and/or motherboard.
Here are links to the error report, dump file, dxdiag, etc.
Does your XPS420 still have the stock/standard PSU?
Mine was having the same behaviour when I replaced the standard 8800 GT with a 3870x2. Going back to the 8800 solved the issues I was having.
I'm trying a 5700 series card next month. The 5800 series draw to much power from the stock PSU, the previous generation 4800 series are even worse.
If you still have the original Dell graphics card and it is having the same behaviour, call Dell asap.