Is the Ribbon completely missing, or can you see the Ribbon tabs? If the latter, click on the down-arrow icon to the right of the Ribbon tab titles to cycle through the ribbon state(s) until you get the one you want.
If it is completely missing, did you try using the RIBBON command, as Dean suggested?
If the RIBBON command does not restore the RIBBON, you might try changing to a different Workspace, and then back again, to see if that forces the Ribbon to load.
If that fails, then you should check the Options dialog, on the Files tab, under the Customization node, to verify that a Main Customization File has been specified. If not, you should add one, most likely the ACA.cuix, using the CUILOAD command.
If one is specified, make note of the file name and location. If the Main Customization file is not the ACA.cuix (or the ACAD.cuix, if you intend to use ACA as AutoCAD), you may want to consider resetting the Main Customization File to the ACA.cuix. (One exception - if your firm has a custom CUIX based on the ACA.cuix or has a custom Main Customization file and uses the ACA.cuix as Enterprise Customization File, found just below the Main Customization File on the Files tab of the Options dialog.) Then use the CUI command to open the Customize User Interface dialog. Select the current Workspace in the upper left pane, under the Main Customization File, Workspaces node. In the upper right pane, you can then examine the Workspace Content, including whether or not any Ribbon Tabs have been added to the current Workspace. If not, you could add any that are defined in the currently loaded customization files.
David Koch
AutoCAD Architecture and Revit User
Blog | LinkedIn
