Usually this occurs when you have uninstalled a second operating and the boot path has been left in the boot.ini file.

1. Press the start button and press run icon . You can also press the Windows Icon + 'R'
2. Into the dialog box that appears type msconfig.
3. Go to the 'BOOT.INI' tab.
4. Press the 'Check All Boot Paths' button.

5. You should then be presented with a screen similar to this, but probably with a different Boot path.

6. Press 'Yes' to remove the invalid line from the boot.ini.

Note: If you have a dual boot system instead of pressing the check all paths button change the timeout value to 3 seconds.