OnePlus X Touchscreen suddenly not responding

Ok so i’ve used my phone for 2 years, no bumps no drops, in a perfectly good condition.

One day the touchscreen suddenly got no response anymore

I’ve tried rebooting, factory resetting, nothing worked

I have some knowledge of phone disassembly but my question is.

What could have gone wrong, the whole screen or the mainboard or the touch sensitivity it self so i could go and change that. I was thinking to order a new screen but don’t really know if the problem is in the screen and i have no idea how to test it

The phone is in perfectly good condition, never dropped once. Here is a picture of the screen.

My question is how do i know which part of my phone is broken so i can fix it.

Thanks for helping