windows 7 - Acer aspire laptop (Win7-64) forgets my settings

I've had a Windows-7 (64) Acer aspire laptop working fine for several years. Occasioanlly it gets used by house quests and people other than myself. Now today when I switch it on, it appears to have forgotten all of my settings, e.g. my background image, my taskbar location, my windows theme, my choice of icons to have on the desktop, and many other things. But all my files are still fine and the computer works, including the wifi connection. I then tried changing all of those things to how I like them, but after another reboot - it forgot them all over again.

Any ideas?

EDIT: I appear to be logged in a "mick-acer" - there do no a ppear to be any other logins. I.e. if I select switch user, my only choice is "mick-acer".

Answer

After much flailing, I found I had a corrupted user profile. Fix here.