Display becomes a blur on exit

I dont think this particular problem has been posted yet but it one that is annoying me... When I exit FSX the programme seems to shutdown and return to the desktop which then promptly becomes a complete blur of lines. I cant make out any icons although interesting my mouse pointer is clear as a bell !! The only thing I can do is turn off my computer and turn it on again.I have reinstalled FSX but it still happens.Any ideas ??Thanks Richard Dell P4 3ghz1 gig RAMNvidia fx5200 (in big need of upgrade !)