Thanks for the info. I talked to my colleague again and what he meant what that I should erase the harddrive with Knoppix and then reinstall Windows 7. I tried this but it didn't work, because Knoppix couldn't access the harddrive with the standard Linux commands. I then tried to reinstall Windows and got the following error message:

Windows has encountered a problem connecting with your device. The error can be caused by unplugging a removable device such as an external hard drive while the drive is in use or by faulty hardware such as a harddrive or a CD rom drive that is failing. Make sure that any removable storage device is properly connected and thenrestart your PC.
status:0xc0000069
info:unexpected I/Oexception

All USB devices are removed,so it is probably the harddrive that is failing. I tried the memtest command, but then I got "memtest could not find kernel image:memtest".
If this is only a harddrive error, it is strange that Nortons software and Windows security updates were blocked. Maybe it is both a virus and harddrive error.