I have a Roku 3 4200X that was working perfectly fine until I dropped the remote (one with a highly coveted headphone jack!) from couch level to the floor and the remote became deader than a doornail. I changed the batteries, took it apart to look for any loose connections on the board, tried to re-pair, etc. but the activity indicator light on the remote just won't come on so it's DEAD.
I then decided to take the working remote from my Roku 2 XS and try to pair that with the Roku 3 following the support article instructions but it just wouldn't work. The remote blinks both green lights but the pairing process takes forever on "Searching..." and eventually fails so I figure the older Roku 2 XS remote won't pair with the Roku 3 for some reason.
I then took the working remote back to its original device (Roku 2 XS) but it was unpaired, so I went through the pairing procedure by first unplugging the Roku. After I plugged it back in, the Roku 2 XS would not turn on at all. I tried holding a paper clip into the Reset hole, changing power outlets, etc. but like you said its now deader than a doornail.
I feel like Big Brother has been watching me and knows that I was looking into buying a new Roku anyways and decided to speed up the process and cause my Rokus to self destruct now I am left with a working Roku 3/dead remote and a dead Roku 2 XS/working remote. Thanks 2020.