(If it works again then stops working again, I'd suspect that Word may be resetting every week or so, since you mentioned contacting the IT department, if these are company/university/etc. computers with restrictions on installations. If this is your personal computer, ignore my comment. If the problem is resetting, then the good news is that maybe all you need to do it reinstall the plugin as adomasven described, every time this happens, but it's very fast to do that once you have identified that problem. Or of course ask IT to change this for you so it doesn't keep resetting.)