A car with a seized engine generally does not crank when the driver turns the key. Instead, the engine makes a single, heavy clunking noise, but is otherwise silent.
One way to check if a vehicle has a seized engine is to turn on the headlights before attempting to start the engine. If the lights switch on normally, then dim slightly when the key is turned, it is a good indication that the engine may be seized. However, a vehicle with a bad starter may display many of the same symptoms as a seized engine, so it is generally best to get a professional opinion before attempting any repairs.