What does upper right hand corner of iPhone 4 logic board do???

I replaced my screen once successfully, as luck would have it (or my clumsiness) I dropped and cracked it again. Bought another screen from iphone4parts, install went fine with one tiny exception: the upper right corner of the logic board (right by head phone jack) cracked off and stayed beneath the little overhang. There is a hole for a screw to go through at the broken corner. The hole rimmed in black on the underside and copper on the up side. I tried to attach image but won't work using my iPad. The phone is put all back together and when it powers up it goes from off(black) to a lit black. Very subtle, can only tell it lit up black if in pitch black room. The phone rings with phone calls, touch screen is unresponsive. I can answer calls in my car using BT or if I plug in mic'd ear buds and answer call with button on ear buds. I can hear text alerts-But it drives me crazy because I don't know WHAT I'm missing, or from whom. I suspect it it is a faulty LCD screen. Before I replace the screen yet again, I want to know what that tiny corner of the logic board is responsible for, is it worth it to fix my 32 gb iPhone 4. (oh, and the phone was fully functional with the cracked screen BEFORE I replaced it-ugh!). Thanks!

 

Well, I bought a refurb iPhone 4 on eBay to get me through either fixing my 32gb or until I can upgrade to the iPhone 5 in October (please, please,let it be more metal and LESS glass - especially all the corners!!!)

I have gone through all the ifixit iPhone 4 CDMA (Verizon) tutorials. They work great for replacing any of a multitude of parts, however nothing on ifixit.com describes what that tiny corner is responsible for. After 10 days wait, I just received my CDMA replacement screw set from applenberry.com (the original screws were getting stripped out) and plan to remove the replacement screen and reapply the old cracked screen. If it is back to functioning then the cracked corner on the logic board is not the problem - but a defective replacement LCD screen. Aaaaaand then I will start again!