How to bring back my drop down menu?

If you are referring to the gray menu bar with the "startup" "reset" Probe, probe angle, workplane etc... its called "Settings" in the View -> Toolbars list of available options.

if you are particular with your menu settings/appearance, i recommend saving the window layout as something like "Master"  that way you could simply reload it with one click in the future.

oooh, you are talking about the menu bar at the very top. aren't you?!  Your window layout settings might have become corrupt.  

Close PCDMIS.

Browse to this location C:\Users\<<YOUR USER NAME>>\AppData\Local\Hexagon\PC-DMIS\<<YOUR PCDMIS REVISION>>\

then, find GBARSTATE.dat within that folder, and either remove it from that folder, or delete it entirely.

Reopen PCDMIS. you should have it back up and running.

Thank you. Last time, the edit window disappeared, I was told to delete this file too.

Thank you. Last time, the edit window disappeared, I was told to delete this file too.