Lower screen, joystick and d-pad very suddenly stopped responding

I recently got a 3ds used, but with no issues other than the 3D slider being broken (I don’t really care about that though). I’ve been using the DS for six months now, with no lagging, sticking, or any hint of a problem, but yesterday without warning, almost all my buttons + joystick + dpad + bottom screen stopped responding while I was playing a game so I had to put it to sleep and then test the buttons on my home screen. (I also tried recalibration, but couldn’t get past the first step since it required the bottom screen.)

Since then, I’ve regained use of the buttons (for some reason, I didn’t do anything to them) but my joystick, dpad and lower screen are still completely unresponsive. They don’t seem jammed, however, just nonfunctional.

Because of how sudden + without warning this was, I feel as if this should be a relatively simple fix (I’m refusing to believe she’s completely done for 😭) so I guess my question is how serious this is, and where to look—do I need to replace something or just check for a loose cable?