iPhone 5c dropped > screen blacked out

I dropped my iPhone 5c the other day and watched the screen slowly fade to black. No cracks or anything, the fall couldn't have been from more than waist high onto concrete. The phone fell with the screen up. I've experienced symptoms that have progressed as follows:

First the screen showed a row of white squares at the bottom and that was it. The phone would still ring and I could still answer and field calls with the headset button. When I plugged it in to my computer it would make the "bong" noise every nine seconds or so.

I turned it off and then on again and the squares disappeared. The backlight was still on, while the screen was still nothing but black it was brighter than nothing at all. I could still answer calls and even attempt to communicate with Siri (who would tell me I couldn't access his/her help until I unlocked the phone, which I couldn't do).

I came home from work to a dead phone the next day, I charged it up and now the screen won't illuminate at all, and I can't seem to turn it on and field calls with it anymore. No matter what I do it will no longer ring or make any notification sounds other than the "bong" every nine or so seconds when I have it plugged in to my computer or an outlet.

I've opened it up with the proper tools and checked the cable connections, everything seems in order. What I'm worried about is the possibility of ordering a new screen/display/lcd unit from ifixit and finding out that there is something wrong with the backlight or something worse.

Is there any explanation for why the phone suddenly stopped fielding calls or even ringing? Is there any explanation for the backlight to stop illuminating the screen, even on a blacked out screen?

Any help at all is greatly appreciated. I'd like to figure this out myself and fix it, but I can't pull the trigger without having some belief that I'm doing something that will actually be productive.