Make sure its getting power. I assume you tried a different reticle cell.

The reticle is just a reticle,.....it's inert. What's not working for you is the reticle diode which is the illuminator. I've had three scopes that had a problem with the reticle illumination and all three were solved simply by removing and reinstalling the diode to restore the electrical contact. Your diode may be bad or there's also the possibility that the problem is in one of the two switches in the system. My guess is that the gain and reticle illumination rheostats are identical and I've seen bad examples of both. It could also be the reticle position of the on/off switch. It could even be wiring somewhere.

I'd pull the diode and put 3v to it to see if it lights. If it lights I'd try to clean the contacts where it threads in. I haven't needed to pull any knobs or switches yet but that's where I'd go next.