Hi,
My PC has for the past couple of days been rebooting itself. Without warning everything I am doing just disappears except the desktop picture. Icons then reappear and I have to wait ages for the task bar to load. Once complete I press Firefox and then the "restore previous session" button. This has happened 5 times tonight already. Any ideas please?

Do you have up-to-date antivirus software on your PC?

It sounds very much like a virus...

You can download a very good AV programme free from AVG

Hi,
I run av regularly also ccleaner, spyware doctor, registry fast and spyware blaster.
None seem to root anything out at all.

If you're using Windows OS, it's your explorer.exe... That task/program ended and then restarted itself. Probably you're running too many programs and the explorer.exe can't handle it anymore, so it rebooted.

If you didn't open other applications yourself, I agree with phoenix267 and probably you need to update/upgrade your AV.

Or, you probably need to minimize the number of programs running in the background. You can do that by disabling the run during start-up or something similar in their options. Some programs you don't really need will be launched and then runs in the background during start-up and they take up too many of your computer's resources. Try launching your Task Manager, go to the Processes tab and check what programs are running. Except for the applications you are running like MS Word or Firefox, the svchost, the explorer, your AV and other security programs, the smss, lsass, csrss, winlogon, ctfmon, services, system, system idle, and of course the taskmgr, the rest you can highlight and click end task.

Hi,
Thanks for that. I use the most up to date AVG running in the background and other av software at different times. I also keep the background stuff to a minimum.
What
I have noticed is that when I try to log onto my email address at Yahoo.com that is the most likely time for things to go wrong. Such as the system slows down or I get "Program not responding".
Would it help if I were to remove Yahoo email and re-install it. I have a feeling this may be where the problem lies.

Perhaps. You can do that.

You can also try typing http://mail.yahoo.com/ directly into your web browser's address bar instead of using the YMail link in your desktop or logging in through Yahoo! and see if that helps...

Just one question though. Are you using AVG Free or Premium? I have noticed that the free version could not detect and/or remove some viruses. I haven't tried the Premium version so I can't say if it is the same as the free version...