Remove the LED from the remote and measure with an voltmeter if you can get any low (+/- 1V) out of the LED when you shine with a light on the LED. If you do not get anything reverse the polarity of your measurement and do it again. If still nothing your LED is broken.
The radio receiver can detect if your remote work on FM around 100MHz..you should hear the code when you press the remote control and bring him close to radio receiver...if you dont-maybe is cristal (455 orsimillar) broken..replace it...
just have a look at the LED with your CCD camera in your mobilephone, this is sure while you're pressing any key, you must see the LED bright if it's ok.