Are you just opening excel or are you opening excel by doubleclicking on a .xls
file in windows explorer?
Sometimes cleaning up the windows Temp folder will help.
If that doesn't help, sometimes the file that contains the toolbar
customizations can be a problem.
Start Excel in safe mode (to avoid loading anything that could cause problems
(toolbars/addins/macros)
With excel closed
windows start button|run
excel /safe
Back to excel to test it.
If that worked, maybe it was a toolbar that went bad.
close excel
Windows|start button|find/search)
look for *.xlb
Rename them all to *.xlbOLD
Back to excel to test.
If it worked, just delete those *.xlbold files and rebuild any toolbars at your
leisure.
If none of this worked, Chip Pearson has documented some techniques to try when
you're having trouble starting excel.
http://www.cpearson.com/excel/StartupErrors.htm