This has many possibilities, and one cannot judge without seeing the actual device. The falling could have damaged it, the dis-assembling maybe .. maybe you stretched, ticked or disconnected something. And I have no knowledge in the device's hardware so I couldn't tell where the issue(s) could be from, and I'm quite sure neither could you. My suggestion is take it a repair shop, let them see what's wrong.
Just my 2 Halalas.
Edit: This thread is now cursed.
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nexus⁴: Stock 4.4 rooted & xposed.