I had exactly the same issue. Internal built in display was not recognised. This is the second time the issue has occured. The last time was about 2 years ago and I didn't know what fixed it. I was using an external display and one day it just started working. Legit. This time I tried all the software fixes... safe mode, PRAM, SRC, software update, time machine restore... nothing worked. I was about to take the back off and and disconnect then reconnect the LVDS cable but Apple support chat said they wouldn't recommend it. Instead I have a genius appointment booked for 7 days time.
THEN...
Got back from England beating Columbia in the world cup (#pens). Was bit drunk. Really annoyed laptop wouldn't work with potential £1000 for a new one. Smacked laptop on the body a few times and shook it around. Screen then worked.
TLDR; hit laptop