2010 15" MacBook Pro unable to recognize internal display, works fine with external
I had similar symptoms on my MBP 13 (mid-2010). Internal display died suddenly and external display worked fine. None of the software or startup tricks did not bring the life back to in-built screen.
Disconnecting and re-connecting the battery connector from the logic board fixed this problem.

Here is the instruction:
https://www.ifixit.com/Guide/MacBook+Pro+13-Inch+Unibody+Mid+2010+Display+Replacement/4293#s7329