Restart your computer.Then Press the F8 key continually once the computer turns back on. Finally you should get to an options menu, called "Advanced Boot Options" or "Startup Options." If you get to the Windows logo, it did not work; reboot your machine to try again. If you find the options menu, choose one of the options. You can boot Windows normally, in Safe Mode, in Safe Mode with networking capacity, or other options, adding Last Known Good Configuration.