Screen problem (bent digitizer flex cable)

My friend's iphone 4 lock button stopped working the other day. It wouldn't click and was not registering any pushes. His phone is out of warranty. Both being curious engineering students, we decided to try to fix it ourselves. We successfully took it apart and found the the lock button nipple that the button sits on top of was broken. We put some tin foil in-between the lock button and the nipple. Then we started to put the phone back together. My friend got in a little bit of a hurry and pinched the digitizer cable between the screen assembly and the casing. I straightened it out and finished putting the phone back together. The lock button now works, but now all the screen shows in a blank black screen (but the backlight is on). The phone can receive calls and is recognized by itunes. We could not unlock the phone or answer the calls. I guess my question is; 1. does this sound like a digitizer problem? 2. is there anyway to just replace the just bent cable or just the digitizer, or do i need to buy the whole screen assembly? 3. where can i buy a replacement part for the lock button nipple.