Not sure, but I think everyone has gta_sa.set. It's located somewhere near Documents in a dir called GTA San Andreas User Files. This file saves graphical settings you changed in-game. If you delete it the game will make a new one on startup and all setting will be back on defaults (what sometimes fixes the problem). I can run GTA: SA normally on my Windows 7 x64. If the above didn't help, uninstall the game and ALSO delete the GTA SA dir in Program Files (/Program Files(x86)/Rockstar Games/GTA San Andreas/). It might work, but if you never added any stuff to that directory (like mods, but also MTA or SA-MP) I'm not sure if it'll fix the problem.