If the TBAR command isn't bringing it up and your certain cadMEP is loaded, then try switching your workspace and trying TBAR again.

If that doesn't work you can try closing AutoCAD, deleting your AWS profile files found in:

C:\Users\YOU\AppData\Roaming\Autodesk\AutoCAD 2017\R21.0\enu\Support\Profiles\

The problem is unlikely to be with Autodesk Fabrication and you may ultimately have to re-install AutoCAD, but try a repair first.