It only works with the front bezel in place. if the bezel was bent, warped, otherwise damaged it might stop working. if it looks fine you can try your luck simply cleaning it.
basically what the bezel does:
https://www.mobileread.com/forums/at...hmentid=139436
if the bezel is either obstructing or not redirecting the IR properly it stops working
of course, it could also be the ir emitter / sensor grid on the mainboard itself. but a simple screen damage should not affect that. unfortunately there is no way to test.
(ie I'm not aware of a software solution that helps debug individual components of the touchscreen, otherwise you could tell where things are going wrong)
maybe this could be done directly in the kernel somehow - no idea if the touch logic is done in software or by a dedicated chip or what