Why can't my valet key turn on the engine?

I've left the car unused for around two months. Tried to restart the car with a valet key when I came back but it couldn't start. I suspected it's the battery so I got it changed and still it will not turn on. My master key was left back in my home country so now i will have to ask it to be sent over. Can it be the immobilizee system that has put the car in a lock mode? Will my master key be able to turn on the car?