First of all, can U reboot ur computer into 'Safe Mode'?
Try follow this :
1. Switch on the computer
2. Hold the F8 key before it change the windows logo screen
3. As I remember, there is a menu that U can select like this but not sure (1) start with normal (2) start with safe mode (3)..... (4)..... , I forgot (becos I used XP now)
I told my friend that he had the experience like yours and was successfully treated.
I thought that it may be affected by the USB keyboard. I haven't used an USB keyboard before, so I wonder whether the system is able to detect the keyboard during boot up ?