Was the PC showing any performance issues just before this happened?
If you start tapping the F8 key from the second you start the PC does it eventually display a menu, if so use the arrow keys on your keyboard to highlight Last Known Good Configuration then click on the Enter key, let me know if that helps and please post what you see on screen.
If you start tapping the F8 key from the second you start the PC does it eventually display a menu, if so use the arrow keys on your keyboard to highlight Last Known Good Configuration then click on the Enter key, let me know if that helps and please post what you see on screen.