Hi Buteman thanks for reply. Tried Kapernsky and all clear. Event viewer showed critical kernel power failure which I believe is just the windows protection system Kicking in and shutting down the computer. I used to like using Event Viewer in XP but in Windows 7 it throws up so many issues I have stopped using it. I have spent the best part of 4 hours now trying everything I can think of including system restore, numerous malware scans all with no success! However, I am hoping I have sorted it now. I ran CcLeaner in safe mode restarted the computer and fingers crossed seems back to normal. I suspect there was some temporary file creating problem. Ccleaner would not run normally and just crashed causing BSOD but ran in safe mode and seemed to have cleared problem. Ccleaner was not the problem but the solution when run in safe mode. Ironic to think yesterday that I was thinking how well the computer was running and today ran into major problem. I am not good at backing up so will have to focus on this! Thanks again.

I can only think that it was some browser add-on that was corrupted with a malfunctioning temporary file. I use IE9 and Firefox6 and it was crashing in both browsers. I have never experienced attempting to clear temporary files causing a shutdown before. I would have expected to have found malware but non shown up.