DiverTim

Thanks very much for your help. I had multiple Firefox and IE sessions each running in safe mode and it didn't freeze up. As a negative test I then tried to launch Firefox in standard mode and my screen froze almost instantly, before it had even launched. In Firefox I appear to have had 3 plugins which 'Always activate' - Active touch general plugin container, Open H264 video codec and Shockwave flash. I have changed Open H264 to 'Never activate' and the other 2 to 'Ask to activate' and when launched it frozen yet in standard mode - so fingers crossed.

I'm running Vista Home Premium. My screen occasionally freezes and stays frozen such that I have no option but to turn the PC off and on again. Usually (but not always) it's when I'm doing something in a browser. It happens with both IE and Firefox. One particular website which seems to make it happen with reasonable repeatability is www.bristolzoo.org.uk/ A few days ago I ran 'sfc /scannow' which reported it had fixed a few files and for a while I thought it had fixed the problem but it hadn't. I had task manager running when it last happened and although neither the CPU or Memory usage graphs were anywhere near maxed out, the Task Manager icon in the system tray was showing all green in the frozen screen. I suspect it was maxed out but only had time to show this in the small system tray icon before it froze. I have just run a wize registry cleanup in the hope this would resolve it but allthough it found and fixed numerous issues it didn't resolve the freeze up issue. Browsing the Bristol Zoo website froze it once again Operating system:Windows Vista Home Premium (32 bit) Service Pack 2 System root: C:Windows Available physical memory: 3070 MB CPU: AMD Athlon 64 X2 Dual Core Processor 5000+ Drive Info: C: 455.33 GB D: 10.43 GB Internet Explorer: 9.0