When I try to restore from tools or help I get no response and the System Restore tab has vanished from my Properties box. Could someone please help?
Thanks,
Doug

Try in Safe Mode.
It may be also a sign of an infection.

Thanks but that doesn't help. It's not there in safe mode and it's missing some of the registry keys as well.

Try this: http://windowsxp.mvps.org/repairsr.htm