I had windows 7 installed on my machine and because of a virus infection, I had to format my C: drive and reinstall the operating system. The disc seems to install windows 7 fine, but then when I go to start windows, nothing happens. The 'starting windows screen' appears but then it just leaves a blank black screen with the mouse cursor. I tried again with all external usb drives/cams taken out and also ran a memory diagnostic, but it didn't help. What could be the problem?