A friend of mine has a very similar problem to the guy in this thread click here
It looks a though he has had some type of virus, since cleaned up but has left his desktop background with a spash-screen type of thing advising him he needs to run an adware scan ( or something similar) - -when he starts his PC this appears and worries him so much he switches it off !! I have found no viruses/ trojans - but am unable to change the desktop background. When attempting the fixx in the link above, I cannot type anything in the "open" box after selecting start, run - - the place where you type "regedit". If I go into a DOS prompt, I am unable to type anything there either. Trying to boot in SAFE mode is not possible, F2 on boot does nothing - and I know this is the way its done on this particular PC.
Any help appreciated - - though I'm not being rude if I do not respond right-away as I have to go to work soon.