I'm not sure it's worth that much, but...

(1) If you have Windows XP, open excel and go to "Help" then "Detect & Repair"

(2) If that doesn't work, - close all programs - hit "ALT" "CTRL" & "Delete" at the same time - that will bring up your Windows Task Manager - see if you are running any programs in the background. If there are any, check them out.

(3) If that doesn't work, run a scandisk & diskfragment, then shut down and re-start.

Don't worry, the image below will not happen: