Are ther no lights at all them. I guess you should have at least the power light on with each one. If not, maybe the mains socket itesf is no longer live for some reason. You could unplug the offending one and try it in a known good power socket.
PS - just saw this guide.
Hmm, it does kinda sound like it's expired (met it's maker), unless someone else knows a good trick to get it going. Sorry I cant help you any more than this. Stupid question, but I don't suppose you could run a network cable instead could you? Much more reliable... Looks like you're not the first with this problem:
If you swap the PLA's over and press either the reset button or if there is a pin reset do this whilst plugged in. As in the previous comment fron @Walter25, there should be at least a power light on at least one of them, unless a power surge or something has killed them both.
Regarding the replacements, Where and when did you get them from, (I.E. Did you get them from TT or somewhere else ?) What make and model are they?
I have escalated this for OCE support for you and they will respond here.
Could you please ensure that your community profile includes your PHONE NUMBER as OCE's will need this to tie up your screen name to your account. (click on your avatar to view the information > Settings > Launch Profile Wizard,put your phone number in box, then scroll to the bottom of page and click save)
"Both adapters where supplied by Talktalk 2-3 years ago when the Talktalk TV box was first installed.
Both adapters show no lights whatsoever"
Apologies for this. The warranty period for this would be 12 months.