Use the System Restore command prompt when your computer won't even start in Windows Safe mode. If you are unable to start your system in Windows Safe mode, there's one other thing that you should try before you decide that it's time for a new Windows incarnation on your machine.
You want to avoid re-installing Windows, because this usually means that you loose all your files, documents, internet explorer favorites, mail messages and so on.
Instead of a normal boot in Safe mode, as explained in our System Restore in Safe mode tip, you can also choose "Safe mode with command prompt" from the "Windows Advanced Options menu".
That starts cmd.exe instead of Windows Explorer. It also means that you will have to type in commands at the command prompt, but ...
... it could also mean that you can recover your computer without losing your data.
You need to log on with the administrator account or with an account that has administrative credentials if you want to use the System Restore command prompt.
Once your machine is started in Safe mode with command prompt, type
"%systemroot%\system32\restore\rstrui.exe" (without the quotes).
This will launch the System Restore wizard. Choose the option to restore your computer to an earlier time and select a good restore point to try to bring your computer back to life.