I have had this problem before many times. Try letting the PC boot into windows (blindly with the screen still blank if it is) and press CTRL+ALT+F4.
That "should" work otherwise, try CTRL+ALT+F1 and wait a few seconds before going through to each other F functions until you reach F8.
eg: CTRL+ALT+F2 - wait a few seconds
CTRL+ALT+F8 - wait a few seconds
Hope that works for you