File closes without prompting to save
 

My boss has an Excel file that closes when she uses the X to close. It does
not prompt her to save it. When she attempts to re-open the file it says it
is already open. Is this a problem with the file or is there a setting
somewhere that may be affecting that particular document. It does not happen
on other documents.
It is saved on her desktop... I know I know bad idea.

ANY help is appreciated.