Ok, here's what you do first. After reinstalling run the game if it works, good, else tell me when the game crashes. This happens most of the time to me, it crashes on loading after it reaches 75%. I dont know the exact reason of why this occurs but here's the solution to it. After you are done with installing the game and SA:MP, rename your "Rockstar Games" folder to something like "Rockstar Game2". This solves this problem 98% of the time. If it crashes on start, its most likely that your gta_sa.set messed up.