Erm, that's not good. The wallpaper change disabling is a symptom of
SpySherrif, and it's a pre-emptive action, before it starts setting your wallpaper to "VIRUS INFECTION".
There could of course be another explanation, but SpySherrif is the most prominent cause I know of - I got infected by it a while ago after a dodgy download, and it will take your whole system down to get it off your machine. But it is fixable. Investigate whether you're infected with SpySherrif ASAP, so you can attempt to remove it before it does anything more exotic...
EDIT:
http://www.thespykiller.co.uk/files/cleandesktop.exe is the desktop clean you're looking for, if you want to try that before assuming it's anything else though
09-f9-11-02-9d-74-e3-5b-d8-41-56-c5-63-56-88-c0