First, make sure you've downloaded the latest patch from:

http://www.ehuman.com/patch/ta/620_pc

There have been issues with the code that launches the Tooth Atlas (which is what's run when you click on the desktop shortcut), so try bypassing the launcher altogether. Go to C:\Program Files\eHuman\Tooth Atlas and double-click on the START file.

If it opens in Internet Explorer, you'll need to instead right-click on the START file and choose to 'Open With...' our BHI browser. If you choose the option to open all files of this type (.bhi) with the BHI browser, in the future it will open correctly.

If this works, we recommend you replace the launcher shortcut on your desktop with a shortcut to the START file (if you right-click on the START file, you'll find an option to create a shortcut).