I can not run Theme Park in fullscreen mode on Windows 7, I've tried to press alt+enter while in game, I've tried running it as administrator, I've tried closing down pretty much everything on my computer and running it in compatability mode but nothing works.

Anyone know how to fix it?

It could be a firewall or security related issue. Make sure the game is not restricted by any programs. While disconnected from the internet, you could temporarily turn your firewall off to see if that makes a difference (remembering to turn on again), or try running the game with the most minimal of programs running in the background.

I have had keyboard control problems before whilst running games, but they were oddly related to having working but not 100 percent compatible USB console joypad adapters connected to either vista, 7 or 8 at the same time.

Have you tried clicking on theme parks 'graphic mode setup' shortcut, and selecting full screen? I would try experimenting with the options there also, or as a last resort reinstalling

use the included configuration utility to change the output device
(overlay/opengl/etc)

I actually just had to inactivate my Anti-virus program for like 10 minutes, just to start the game and then full screen worked. I thought about trying it earlier but I didn't think it would prevent the game from running in full screen though. Thanks for all the tips, it was very helpful and I'm sorry for being such a newbie.