Excel Will Open Some Files But Not Others
 

Have new iMac w/ OS 10.6.6. Installed older version of Excel (2004). Worked fine. Opened files, worked on them, no problem. There are 5 files, though that won't open. Tried double-clicking and get a "flash" of the loading bar but nothing opens. Went to menu bar: File, Open, find file name, etc....