3 Answers

If the problem is just the remote control, you can call the manufacturer and have the remote controls replaced for around $75.  The name can be found on the unit itself.  Google the phone number by entering the name.  I did this a couple of years ago.  However, if it's over 15 years, you may consider getting a new one at Home Depot starting at $250. 

http://oazeeeawa.jugem.jp/?eid=27 

http://www.fixya.com/support/t5373778-chamberlain_102_1499a_opens_w_remote

You should first check the beam, to insure that 1. nothing is in the way of it, 2. make sure that they are aligned, you can adjust them back to each other if needed.  Next, I would see if anything is preventing the drive from moving, something jammed into the chain drive?  Pull the safety release on the chain over the floor of the garage, usually has a red tag/handle on it.  This will disengage the door from the opener, only do this if door is in down position...   Without the load on the opener, try it and see if it will work now.  Check the website for your manufacturer, and look up troubleshooting if this stuff doesn't help.