Sometimes your software will require updates to be made; if you are running your Excel program and it is not up to date this could be causing a problem. Start by updating your software.
1) Close all open programs.
2) Open up your control panel.
3) Click System and Security.
4) Select Windows Update.
5) In the left hand pane, click change settings.
6) Under Important Updates, select Install Updates Automatically.
7) Select any other options and remember your computer has to be powered on at the time of the scheduled updates.
If updates are not the issue, make sure you are opening the files using the correct program. You can see which programs you can use to open that file by right clicking on the file itself. There should be an "open with..." option which when clicked on will show you what options you have for opening that file. Some computers come with software preinstalled (like Mac comes with a .pdf reader) and you may be able to use another program.
If updates don't help, and you have no other options for opening up your Excel file, contact IT at email@example.com, or 617-349-8770.