I was given this answer via another forum (Computeractive). It worked for me.
"Try running System Restore after booting to "Safe Mode with Command Prompt". Immediately after powering on, tap the "F8" key ("F5" in some PCs) until the Boot Menu appears. From this select the option to boot "Safe Mode with Command Prompt". Once booted, at the prompt, type:
%SystemRoot%\system32\restore\rstrui.exe and press Enter.
This should open the normal System Restore window from which you can run it."
Hope it works for anyone else trying it.