Boot into safe mode (press F8 as the machine is starting) and change the resolution of the display to a low setting. Reboot. If that doesnt work:
Boot into safe mode, go to device manager (right click on my computer, select properties, select hardware tab). find your video card and right click on it and select uninstall. It will require a reboot.
The drivers should automatically re-install on reboot and ask for another reboot. Should that not work, you may need to install from your disk or download from the net.