I have 2 liftmaster 3245. The hand held remotes were working fine then stopped. I replaced the batteries and turned of all electrical/RIF close by. Still not working. Both cars operate the doors with no problems as does the wall mounted controls. I then unplug one of the units, still no luck, does anyone have any knowledge to fix this...

You need to reprogram the remotes by briefly pushing the learn button on the garage door opener until it flashes once, then release the button on the garage door opener.

Now press the remote button once until you hear the garage door opener click, now press the remote button once again and the remote should be programmed to work for that garage door opener.

DO NOT press and hold the garage door opener learn button for more than 10 seconds or you'll erase all programs and have to relearn all the remotes, including your car ones.

Hope you found this very helpful and best regards.