Yes, I disabled anti virus (not sure about Admin, but I am only user and have all permissions).
I am in contact with tech support who advised:
1) Using the programs and features control panel remove all versions of TurboCAD, TurboCAD Plug-ins and symbols installs.
2) Delete all of these folders.
C:\Users\your user name\AppData\Roaming\IMSIDesign
3) Download new installer (from link given), and activate using original serial number.
Unfortunately, so far, it won't accept the original serial number.
Am waiting for further instructions after the weekend.