Closed down last night with the usual "installing updates" that I don't seem to be able to prevent - and today it loads up IE instead of Firefox, installs Google toolbar etc, and seems to have zapped all my cookies and remembered passwords. When I went back to Firefox, all my bookmarks had gone.

Also removed half of my desktop, and changed the background. It has taken me an HOUR just to get back into a few apps and sites. Is there any way I can guard against this in future?
I don't want to turn on my other machine in case the same thing happens.