One of the most common reasons for the Access tab dissapearing is that the AOI add-in has been disabled in Microsoft Excel. This can happen for a number of reason, however, the most common is as a result of a Windows Update.
To check and re-enable the AOI add-in:
Open Microsoft Excel.
Navigate to options (this is usually located under the File menu).
Select Add-ins.
At the bottom of this screen, next to Manage: change the drop down to Disabled Items and select Go.
Click on Access Office Integration for Microsoft Excel and then click on Enable.
Close Excel and then re-open and you should now have the AOI menus available.