Word is missing something (or some things?)

The MLA style should have been installed along with the rest of Office. Look in the folder C:\Program Files (x86)\Microsoft Office\root\Office15\Bibliography\Style, where there should be 12 files with .XSL extensions. One of them should be MLASeventhEditionOfficeOnline.xsl.

If you don't have the full set, go to another computer that does have all the styles, copy them to a USB drive or similar, and paste them into the same folder on your computer. If you don't have access to another computer, try doing an Online Repair of Office (in the Control Panel > Programs & Features, right-click the Office 365 icon and choose Change from the menu).

I looked in the folder you specified, and the MLA style IS there. However, it is not in the drop down list in Word, the other 11 styles ARE there.

I also copied the MLA from another computer and pasted into the bibliography folder. Again, MLA is still not showing in the drop down in Word.

Then I did the Online Repair as you suggested, same results.

Here's another location to check. The files from the Program Files (x86) location are supposed to be copied automatically to this one, but maybe something is interfering. Type or copy/paste the following into the address bar of the File Explorer and press Enter:

%appdata%\Microsoft\Bibliography/Style

If the MLA file isn't there, copy it to there from the Program Files (x86) location and restart Word.

Jay-

In a search of the entire C: drive, there is no %appdata%\Microsoft\Bibliography/Style folder

Apparently I did not follow Jay's instructions properly -- my apologies.

I typed it into the address bar and MLA does show up, however, all 12 styles are located only in the C:\Program Files\Microsoft Office\root\Office15\Bibliography\Style, NOT in the Program Files (x86) location. The Microsoft Office string above is not in Program Files (x86) at all.

I to am having the issue. I tried both solutions. and nothing has worked. I looked in my files and it shows up there but still cannot get it to recognize in the drop down menu. I even tried opening up the mla format new page and it still doesn't appear in the drop down menu.