If your computer blue/black-screens, it's likely you'll boot into the automatic repair screen from that screen:
- Click "Advanced Options"
- Click "Troubleshoot"
- Click "Advanced Options"
- Click "System Restore"
It should bring up a system restore window
Click next to see the Restore points
Select the date that was before the computer stopped working
Hit continue/next/finish on all prompts - it should reboot in 5-10 minutes and go back to the sign-on screen