Hello...my PodXT Pro is acting up. 

Essentially, a doorstop as it sits right now, although it provided several years of honorable service. It basically has two alternating behaviors when switched on: Either the signal light stays on, with or without input; or, it doesn't respond at all when a guitar is plugged in. I've unplugged all attachments, i.e., FBV, USB, etc.  Any suggestions, or thoughts? Am I missing probable easy to fix error (i.e., did I push a button and not realize it?)?  Will it make sense to get this looked into, or will the service/parts be outrageous?  I could by a used one at GC for $250.  Thx for any advice you may be able to offer.