Bootcamp: Black screen shows after windows 10 installation
For anyone else coming here, try this simple solution first.

Disconnect the power (MagSafe plug). If the display comes on, it means your power profile is set to turn brightness down when the AC is plugged in.

Solution: While power is unplugged, login and verify that the brightness controls work. Then plug power in and turn the brightness up. For some drivers, those brightness control don't work, and I've seen drivers that install with brightness set to zero by default.