1. Your battery is dead and needs replacing. -- Replace battery
2. Your battery is simply dead because your generator/alternator has gone bad and is not charging the battery. -- Replace generator/alternator and charge battery.
3. Your starter solenoid has gone bad and will not activate the starter. -- Replace starter solenoid.
4. Your battery cables are loose or have corrosion build up and are not allowing the battery to charge or provide power to the other components. -- Clean and tighten battery cables.
5. Your battery has a very low level of acid/water mix inside and is not charging or providing power. -- Add distilled water to top up fluid inside the battery.
6. Your vehicle (if it has an automatic transmission) is not in "Park" or "Neutral"...or...if it is a stick shift, the clutch must be depressed to start. (Not sure they had this safety feature in 1965). -- Place vehicle in "P" or "N" or depress the clutch and attempt to start.
and last and by far the worst,
7. You have encountered an invisible cloud of Killacar radiation. -- You must push your car clear of this cloud before it will start. ;-) jk