Hi Rotherboy,
Thanks for posting in Microsoft answers!
Firstly, I’d suggest you to uninstall the antivirus program and try to perform a system restore and check if that fixes the issue.
Refer the link below for more on uninstalling programs:
Uninstall or change a programhttp://windows.microsoft.com/en-us/windows7/Uninstall-or-change-a-program
If the above steps do not help, try doing a system restore from safe mode and check if that works fine.
Refer the below link for more details on starting your computer in safe mode:
Start your computer in safe modehttp://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode
Let us know if this helps!
Regards,
Gokul - Microsoft Support