If you have something like a Compaq or Dell mfg within the last 4 years they should have a hidden partition on the drive to restore from. You should see an option early in the boot process prompting you to hit a key (ex. Ctrl+F11 or F10) to restore the computer.
The make and model should be listed on the front or back (like Inspiron 520x), unless it's a custom built PC, not from a major manufacturer.