Check the starter, if it doesnt turn over. Try tapping the solenoid with a hammer, or getting power straight to it. If it still doesnt turn over, it could be lots of stuff. Is your bottom end seized? Try spinning your crank by hand. If it spins freely, then you can rule that out.
How are you sure its not the battery? Have you tried another battery? Does it make any sounds/clicks at all when you try to start it? more info