how can i fix my pug 206?

i have a peugeot 206 today i drove it fine but when i tried to get bk in the central locking didnt work so i opened the door manualy put key in ignition no power atall its not the battery it was left 4 a short while so i tried to use central locking which then worked and the car decided to start but then when i stopped tried it again a while after it did it again,could anyone give me an idea on what to do? i was told it was the immobiliser so any info gladly recieved ty tracy