I've tried a few System Restores and it's not helping. In fact the problem started during a Restore, which crashed the PC and on re-boot, the thing hung and has been exhibiting this (potential) problem since.
Also, my system doesn't have Windows update Q811493 to remove :-(
Sometimes I can log on to the other profile easier than mine. If I then try to "Log on as different user" while the first profile is up and running, the PC simply crashes.