Are you getting an error message? Does it happen with all reports, or just one? And, does it happen with other database?
If it's only happening with one report, try creating a new report based on the same table/query, and if it works, delete the old one.
If it's happening with other reports, or even other database, then the problem might be more serious. I would try re-installing Microsft Office. If you do this, make sure you check where your Office files are being saved (i.e if they are inside the Office directory, you will have to move them elsewhere prior to re-installing office).
Good Luck.
comteck