Reboot while constantly tapping F8 to bring up Safe Mode. You may be given the option to boot into the last good configuration, so choose that. Otherwise enter safe mode and use the restore program in Accessories.
If you can't boot to Safe mode:
Switch off the power.
Open the box and touch the frame to ground yourself.
Now, reset the BIOS by removing the battery for 20 seconds or more.
Before you power up again , disconnect all cards and peripherals except the video card.
At this point, your machine should be at about the same settings it was at when you bought it.
If nothing has changed, turn off the machine and reboot while constantly tapping the control key to open up the BIOS settings page.
If you can see the BIOS settings, your machine is likely ok but your Windows operating system is crashed. You will need to re-install windows from the windows disk