I reset my firetv stick, during initialization it was stuck at a point, (Audio check) i waited so long, but no change. Many times I tried. Later I found a solution which I had no hope.
To change the battery of remote.
It was a new battery, so I removed and insert the same... God, it solved the issue.
Sometimes solutions are like this, crazy.
I suggest you try changing your remote battery, (put different) may be the chance ony 0.01%, try.