Cannot Open Excel 2007 Files From Windows Explorer

I cannot open MS Office 2007 Enterprise Excel files by double clicking on
them in Windows Explorer. Excel opens, but not the file. There is no error
message. I have to open them directly from Excel, and the file opens just
fine. This problem just started happening. It used to work just fine. I
emailed the same excel files to my wife who has MS Office 2007 Excel, and she
opened it from Windows Explorer. I ran my virus detector, and I have no
virus. I tried opening the file from explorer with the antivirus off, and
still does not work. I can open Power Point and Word files from Windows
Explorer just fine, the problem is only with Excel. Does anyone know what the
problem could be? Maybe some setting changed on my computer? It is a pain to
have to use Excel to open my files. It is nice to got to Windows explorer and
and open from there sometimes.