Most obvious cause is a 99% dead battery which has insufficient amps to turn the starter. The starter immediately drains all the amps from the battery and everything goes dead.
To test ....... fully charge the battery [Halfords battery trickle charger] or get a friend to use jump leads to boost your battery and 'jump start' your car. If it starts on the starter switch, buy a new 12v [heavy duty] battery. If your car is fresh from the garage sales then go back and kick up a stink - guarantee etc. Always buy a 'heavy duty' rather than a standard battery - you will get the benefit on a very cold winter's morning.

If your battery is OK [I doubt it!] there is either a vehicle short to earth, loose/corroded battery terminals, or short-to-earth fault with the starter motor.

NB .... a knackered battery will not take any charge. Consequently even if trickle charged, the battery fails to hold any amps. If suspect get the battery tested by any garage or motor shop. Motor shop batteries are cheaper than supplies from a garage.