MY HYUNDAI ALARM KEY WILL NOT WORK?

I HAVE A HYUNDAI COUPE 02 REG, ALL OF A SUDDEN MY ALARM KEY WILL NOT RESPOND. NORMALY WHEN I PRESS MY ALARM KEY MY CAR LIGHTS FLASH, THE DOORS OPEN AND THE ENGINE STARTS.

NOW WHEN I PRESS THE ALARM KEY NOTHING HAPPENDS, IT WILL NOT RESPOND,HOWEVER I CAN OPEN THE DOOR MANUALLY, BY USING THE KEY, BUT I CANNOT START THE ENGINE WITHOUT THE ALARM SOUNDING,