When you use the work, you probably use the new command from the Window menu to save the new Excel file, so this can happen.
Maybe it's poisoned, and office may be poisoned.
Ii. Approaches to settlement
Locate the installation directory for Office, such as C:Program FilesMicrosoft OfficeOFFICE11, which has a folder with the name: XLSTART
Delete this folder and all of the contents inside, so you can avoid the problem.
In case the above method is resolved, open the Excel file prompts to install what kind of, please use the ② method to solve.
Recommend killing the virus, and then, there are problems, then, please reinstall Office on the line.
Another possibility is that your spreadsheet in the macro virus, you go to the Internet to download a "macro virus kill" software installation and killing, you can solve the problem, pay attention to the 360 anti-virus software to close off.