Error on opening outside of Excel

[ChemistB]

This is the second time this has happened to me. Suddenly, I cannot open an Excel spreadsheet except through the Excel application. This includes through Windows Explorer, on the internet (this forum), in email. I need to save the file first, then open Excel, then open (through Excel) the file.
In Email, I get "System cannnot find the file specified"
On this site, I get "Access to the specified device/path is denied"
From Explorer, "Cannot find the file.... based on the criteria xls(or one of its components). Make sure the path and file name are correct and that all required libraries are available."
Last time, our IT group couldn't fix it and had to reinstall the entire Office package to get it working again. I'd rather not go through that. Any suggestions? This happened both times after downloading xls files from here so maybe some incompatability with other versions?

[shg]

Verify Ignore other applications is unticked, reboot, try again, detect & repair?

[ChemistB]

Thanks shg!!
It was the "Ignore other applications."
good call.