Did you do a cold reboot, or just restart?
For what it's worth, i had this with an older version of desktop manager, but it didn't just happen out of the blue; it started when I upgraded to that version, and nothing I did fixed it until the next upgrade. If it has happened to you just all of the sudden, I'm surprised.
If a cold reboot doesn't fix it, and if you aren't running the latest version, then my advice is upgrade. If you are running the latest version, then do a clean uninstall and then reinstall desktop manager.
EDIT: An afterthought...See http://supportforums.blackberry.com/...ed/td-p/674029
. It wasn't the answer for me at the time, but maybe for you. I have a hunch it is, especially as it sounds things were working until suddenly they weren't.