Just wanted to post this here, if it might help anyone later...
The problem preventing my GC2 from running (which caused me to re-install, which caused all kinds of other errors, but that's a separate story ) was that I changed from an old 4x3 ratio monitor to a newer 16x9 ratio monitor, and the new monitor had fewer lines of resolution (1080, instead of 1200), and GC2 didn't like it, and didn't sense the different resolution. I wound up with just a blank screen.
After re-install, I still had the issue. Started clueing into the problem, so I moved my old user directories (where the saves and preferences go). Then it worked, but only for one chapter (can't remember which one), the other two still defaulted to 1600x1200 and wouldn't work.
So anyway, if you change to a new monitor format and the game just launches to a black screen, find your prefs file, and edit the resolution from 1600x1200 to something else