A lot more info is needed to work on the problem.
Did you install the game from the Original DVD?
What Edition (Version 1, 2, 3.) is the Game. (find it on the Main Menu Screen lower right corner or Box/Disc/booklet.)
Did it ever play correctly?
Did you install any Mods?
Sometimes deleting the GTA_SA.set file in the User Documents GTA San Andreas File works.