w203 keyless entry-how to?

my w203's keyless entry only works with one of the two systems its supposed to be working with. It only works using the: INFRARED System, the RADIO FREQUENCY system is not working-the main reason y i can only lock/unlock the car if i point the key to the infrared window on the drivers door handle.

Any ideas on where should i start??? i firmly believe i do not have to have my car diagnosed by star diagnosis...... its not only very costly in my place, its also unavailable! thanks!

btw, im posting this cz i wanna try to fix it myself.