When I open a particular spreadsheet, it asks me to update the links (which
there are some), and whether I do or not, the spreadsheet won't display.

Excel is open, but does not show a spreadsheet.  I do not see it listed in
the Window menu item to select it, in the list of open programs at the bottom
of the screen, or any other indication that it is opened.  If I try to open
it again, I get a message stating it is already open.  

I have tried closing all the way out of Excel, and rebooting my computer
without any luck.

Other spreadsheets are working fine.

Help!

Thanks!