In order to fix your problem you will need to locate your "GTA San Andreas User Files" folder, you will find it in My Documents" folder.
Then you will open it and delete file called:
This will reset all of your Gta San Andreas settings (but it will keep save games),
then you will just start the game and set your settings like you want for ex. controls
JUST DON`T PLAY WHIT RESOLUTION ANY MORE!
This must work, no need to tnx!