Cannot Open Excel 2000 File.

I presume you are trying to open the document using the Recently Opened file list in Excel's "File" menu. If so, use the "Open" entry in the "File" menu instead and navigate to the pen drive from there - it may be that the drive letter has changed. Another possibility: use Windows Explorer (which can be accessed by double clicking on My Computer) to copy the file from the pen drive to the desktop and open it from there by double clicking on it. If that still doesn't work (but the copy worked OK) then right click on the file, click on "Properties" and see if the Read Only box is checked. If so, uncheck it.

And yet another possibility: after closing the file, did you pull the pen drive from the PC without telling Windows to eject it first? If you just remove the drive too quickly, without ejecting it first, the file can easily be corrupted.