1999 Mitsubishi Mirage mileage 80,000. We just changed the alternator and jump started the car. After a couple of minutes the engine light came on, the car beeped three times and then the car shut itself off. The car can't be restarted. We jumped it a second time with the same results.
When a battery is disconnected or goes dead and then recharged, the anti-theft security system is activated causing the symptoms you described. Try locking and unlocking the car with the remote or with the key in the driver side door lock. This should reset the security system.