You also mention you can't change channels, is that referring to a cable/satellite box that also can no longer be controlled?

If you have a RTI processor verify it's powered up and if so try rebooting it. Make sure you see the antenna light flashing when you push buttons on remote.

If you have IR target and emitters check the target is flashing when you press buttons on remote.

Either way check the IR emitters are properly placed on the equipment. Even being half of an inch from where it should be will cause it to not work!