Computer Shutting Down

You might also want to examine your System logs - try to determine if a service is causing an error and rebooting your machine. For a number of "Critical" services, Microsoft default when they screw up is to simply reboot the computer with little/no warning. If that is the case, you can set the service to simply restart instead of rebooting the entire machine to give you some leeway to run some kind of anti-virus/security scan.

I would carefully examine your system with an antispyware/malware and antivirus suite. If you're still having trouble after that, you need to pull out the big guns.

Restart in Safe Mode.

In System Properties--Advanced--Startup and Recovery--Settings, make sure Automatically Restart (under System Failure) is not checked.

Scan with fully updated AV and Spyware scanners, deleting any items found. Rescan do make sure no problems found in second scans.

If the malware which has disabled Norton has broken parts of the software, you might have to uninstall/reinstall Norton (tricky since their uninstaller doesn't remove everything, thus causing the reinstall not to work properly).

If all else fails, a reload of the OS may be necessary.

Run the scans in [b]Safe Mode[/b] that is far more likely to pickup and remove the problem.

Also disable the firewall side of Internet security before performing the scans.

Col