Moved the thread to GD Community (where game problems like glitches and such go).
Although Lite, Meltdown, World, and Subzero are free, the full version of GD is not (it's only a couple dollars though). Anything claiming to be a free download of the full version isn't a real copy of GD but hopefully isn't anything worse, like a virus, although it would explain why the game won't open for you.
--Jayflight/Jayfrost-- Around GD since 2014, forums since 2017 (even though my account doesn't show it!). If help is needed on a thread, just tag me as "@ exosphere" (without the quotes or space) and I'll respond asap!