First of all, check whether any lights blinking or not when u pressed the buttons. Then if none, change the battery, and at the same time clean all the contact points so that u wont have to open the remote key many times. if there any blinking after u have done the previous step, try to reset the system. Follow the next step for the resetting the remote key :
1) Get in and close all doors.
2) Turn on the ignition to 1 and turn off within 5 seconds
3) Remove the key (do not keep it in the ignition as someone suggested).
4) Hold the key up near your left shoulder (this is so it is closer to the remote reciever antenna - someone else suggested this as well)
5) Hold down the unlock button (which is button 1 on my key) and press the lock button 3 times (center button on my key). Release the unlock button and the doors lock which confirms the operation.
If this process is failed, or it works for a day or less only, then u'll be facing the same problem like mine for the past one month.
Somebody in mudah quoted me a full set of key will be RM800+ at Kota Damansara. Hate to invest that much so until now still trying to rectify what is the actual fault.