When TC is closed, delete the Built-in folder, TC will rebuild it again when you start next time, but in Default mode, so you will have to remake your cfg ( Workspace, UI etc) if you have any special system made for it.
Still not work, try a repair by running your instal file again, you get the options of Repair during the install
If that not work, copy/ move out your cfg and template and what else you may have saved in standard folders like Drawings, Library etc.
Close TC, then delete the folder for DL 2016 in
C:\Users\YOUR USERNAME\AppData\Roaming\IMSIDesign\TurboCAD 2016\
But again, make sure you take care of what you want to save before doing this.
This is like a New install for TC,
If you have some special render setting set up you maybe dont want to do this as even if you copy them Out and back again they will not work i have been told from another guy here at the forum, i never do any Advanced renders so me it's not important at all.
V18, V19, V20, V21, 2015/ 16/ 17 Pro. Platinum
Deluxe V20, V21, 2015/ 16/ 17
Windows 10 Home Premium 64 bit, 32 GB
NVIDIA Geforce GTX 780m, 1 GB