NOTE: These will only work if you can get into the system. They will not work if you can't even get into Windows.
In Windows versions prior to 10, you should be able to...
- Go into "Control Panel" and then click "Recovery."
- Next click "Advanced Recovery Methods."
- Now click "Return your computer to factory condition."
If you cannot get into Windows, then on booting the computer try hitting/holding the F11 key to get into "System Recovery". Should that not work, then the option may not be available on your device. If that is the case, then you will need a CD/DVD/USB with the installation media.
For more info on how to do this on multiple versions of Windows, try reading the following... https://neosmart.net/wiki/windows-system-restore/