If the computer only has one account and you cannot get to a command prompt you can try enabling the hidden Administrator Account. Follow the steps here but to not reset any passwords. If this password was a Windows Live Account there may be a problem. You can get the latest version of the software here. Once you have logged into the Administrator Account, use that to undo the System Restore. You will need to disable Secure Boot and possibly enable Legacy boot in order to boot the utility.
Sometimes you can force Windows into the Advanced Options mode by doing the following. When Windows 8 shuts down it does not really shut down like WIndows 7. It is more of a hybrid shutdown. Getting into Advanced Options should let you undo the restore point. See link above.
- Hold the Power Button for 5 seconds or until the computer completely shuts off.
- Press the Power Button to turn the computer on.
- As soon as you see the rotating loading circle, press and hold the Power Button until the computer shuts off.
- Repeat this process 2 or 3 times until you see the Preparing Automatic Repair screen.
Edit: Once you get into the Adminstrator Account you can change the password of your client's account if it is not a Windows Live password.
Edit Edit: If the customer did have a Windows Live account for logging in, you can reset it and then use that to log in avoiding doing any of the above. Sorry I forgot to mention that.
Edited by JohnC_21, 12 February 2015 - 10:47 AM.