Well to make this short and sweet, I was trying to download custom tracks, but it wasn't working so I deleted all the spots for beta and all the things I tried to download in my game files. Now every time I try to open my game it won't even bring it up. It just says MX vs. ATV Reflex has stopped working or something like that. I really need some help because its making me mad >:(
Install this...
http://www.reflex-central.com/savegame_mod.php
If it still doesn't work then you might need to re-install the whole game. Maybe you deleted something from the base game by mistake.