Here is a bit of advice...
I see you are now using the Trial Version...
You said that you bought a new version...
If that is true you need to follow the directions and get your 3dgs key in the right folder...
Then, as 3run says... get the Lite C version of Mystymood...
Then, I suggest you do a "Save As" and rename your project...
Then, In the Main .c file you need to change the file that your code will launch to match the save as name....
Then, start editing by swaping out Mystmood files for your own...