I have even tried several different TVs and HDMI cables.
If you have moved the Premiere to different TVs and used different HDMI cables, then you can safely assume it is a device issue. (not a setting or a TV issue.) As long as you are running directly to TV, no amps, no receivers, etc. I was initially thinking maybe you had mistakenly toggled the TVs internal speakers off or accidently muted it with the tv remote (You'd be surprised...). And you are sure you can't raise the volume with the tv remote (not roku remote)? All up to date with latest software 9.4 build 4200?
However, there are reports in the forum that it sometimes self-corrected with no user intervention. Try unplugging your Premiere completely and let it sit for awhile. Arbitrarily, give it an hour or more. (Let it cool down and discharge).
If this is a new purchase, return it. If an older premiere, give it a chance to repair itself. Myself, I would hope for the best and prepare for the worst. I think my Premiere is about 3 or 4 yrs old, running consistently and no problems, they are a good device in my opinion. Yours may have just quit early. Just a circuit board with solder joints after all.