I think you are referring to the same thing that happened to me a while ago!
I was using Firefox back then Version 1.0.7, I still am but I am now on version 1.5
I solved the problem by uninstalling Firefox, rebooting, running a registry cleaner and reinstalling Firefox.
It seemed strange how it happened in the first place as I had no BSOD and nothing else went wrong to make this happen.
If you are not using Firefox, I can't advise you - sorry.