reinstall your gpu drivers making sure to select your gpu's audio driver and whatever the ”fresh/complete reinstall” option.
why?
because the index receives audio data from your gpu by way of displayport, and for some reason in some setups this driver or its config b0rkify randomly.
if this happens again after you do what i recommended to do above:
if your cans² play audio, but when you disconnect the thing in the headphone jack hole on the index the index's ear speakers don't got no thump, we'll have to take so shit apart, yo, with our trusty t6 torx screwdrivers.
hopefully we didn't need to try and follow that last bit because reinstalling/updating yo6go=pu's fucked up driver stack took care of everything.
good luck, and let us know how it goes :)
footnotes
1: buy the pair as it's nearly always better to have a spare, especially when the difference between 1 and 2 is a lot less than 1.
note: these are 3 pole and won't pass on a microphone signal if you, in your infinite wisdom, decide to do something really weird and and use the comparatively terrible mic on a set of trashcans.
--=
2: slang for over-the-ear studio headphones in specific. in this case, it sits in (somewhat impolitely [apologies: it just fits better] for any set of headphones/earbuds/whatevers.