Warpigtrev

Hi, I am new to the Galaxy, just brought my first, its a diesel 04 plate 1.9, real tidy, problem i have is that the main key with the buttons on it locks and unlocks the doors but when i put it in the ignition and try to start the vehicle it turns over starts and dies just as quick, i know all about the turn 3 times press this and that, which i have done but i stays the same, it worked perfectly, locking, unlocking the doors and was the main key i have used to drive the vehicle until i changed the battery, has anyone got any suggestions please ??