The 4200 was released in March of 2013, so it's getting along in electronic years. It is still officially supported by Roku, in that it still gets updates. But it won't run some of the latest channels, it's a slower processor, and only outputs 30 Hz at 1080p (it does 60 Hz at 720p). There's a reasonable chance that it has simply failed.
Of course, if you're satisfied with the 4200, you could just replace the remote. The Roku web site says the Voice Remote (out of stock) and the Simple Remote both work on your player. The Simple Remote is IR, not wireless like your current remote. IR remote batteries last a very long time, as they do nothing unless you press a button. The wireless remotes are always in communication with the player, although they do have a low powered sleep mode. That is likely where yours has failed. You can also find universal IR remotes in many local stores, as long as they list Roku as a supported device. Just remember you must have a direct line of sight between the remote and the Roku with IR.
Since your remote has the listening jack, it's possible that something has jammed the switch on the jack that is enabling the internal audio amplifier. That would be the same as leaving headphones always connected to the remote. It leaves the amp on at full power, and will drain the batteries in days. You could try inserting and removing a plug in the jack and see if anything dislodges. Do this rapidly a number of times and it might un-jam the switch.
Dan
Roku Stick (3600), Ultra (4640), Ultra (4670), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.
