To remove follow these step's closely, go to start\find\files or folders type in the box Geoshell click enter key delete all the entry's it finds with Geoshell in it. Next go to start run type regedit and press enter, go to menu under edit click find in the box type Geoshell and press enter it will bring up only one entry at a time, press delete key then click ok to confirm to go to next entry press F3 and delete do this until you get to the end of the registry. DO NOT TOUCH ANYTHING ELSE IN THE REGISTRY other than Geoshell then reboot your computer
Overnight inspiration! None of the suggested methods worked because the program re-loaded at startup. So the answer was not in the Registry, but the program files.
I drilled down into C drive, Shell,GeoShell... lo and indeed behold, there was 'Uninstal Geoshell'! Within seconds it was gone!
One thing still puzzles me. I was using Find in the Registry by 'ctrl+f', but this is not the same Find as in the Start menu, so I couldn't look for the Uninstal that way. And Windows Explorer was not to be found, either.