I would suggest detaching any unnecessary devices from the computer and first checking ways you can access the computer.
Try run it in safe mode. On startup, keep pressing the F8 key until the Windows Startup menu appears. Then selected Safe Mode.
Can you start up on safe mode?
If you have the installation disc for your Operating System, you could use the Recovery Environment. Start the computer with the disc in, press a key when the message "Press any key to boot from CD or DVD
". appears. Choose Repair your computer or press 'R' to use the Recovery Environment.
Can you access the Recovery Environment?
If you can access one of those you will have a better chance of repair.
Let me know if you can access them or not and we can continue depending.