Try this:
Look at #5 first.
1) While the base unit is turned off, remove the batteries from the base unit and reinsert them.
2) With the base unit still turned off, remove each of the three memory cards from the base unit and reinsert them, making sure you can hear them lock/click into place. (Also, try the memory cards in different slots to determine if the problem may be with the cards and not the base unit.)
3) Turn the base unit on and select a sound, making sure the remote is at least a few feet away from the base unit. (If it’s too close, it may not signal properly.)
4) If you think the problem is with the memory cards and not the base unit, please take a Q-Tip and some rubbing alcohol and clean the brass contacts on the cards. Occasionally there will be a slight residue on these contacts, and oftentimes, this is all that is needed to get them working.
5) If the preceding steps do not work, re-synchronize the remote with the base unit by taking a pin (or a paper clip that’s been straightened out), and inserting it in the small hole above the battery compartment on the back of the base unit. While pressing and holding this ‘reset button,’ push a button on your remote and hold it for three seconds. This will reprogram that remote to that particular base unit and reset the caller.