Connect an external monitor. If no problem on the external monitor that would indicate a screen pronlrm on the built-in screen,If problem on both:
- Try resetting the SMC and NVRAM/PRAM
Intel-based Macs: Resetting the System Management Controller (SMC)
https://support.apple.com/en-us/HT201295
About NVRAM and PRAM
https://support.apple.com/en-us/HT204063
- Try starting in Safe Mode
OS X: What is Safe Boot, Safe Mode?
https://support.apple.com/en-us/HT201262
- Boot to Recovery and repair the startup disk
OS X: About OS X Recovery - Apple Support
https://support.apple.com/en-us/HT201314
- If it is repairable reinstall the OSX
How to reinstall OS X on your Mac - Apple Support
https://support.apple.com/en-us/HT204904
- If you do not have a backup use disk utility to restore the internal disk to an external disk so you can try to recover data.
Then format the startup disk and do a fresh install of OSX
If still problem, make an appointment at the Genius Bar of an Apple store since it appears you have a hardware problem.
Apple Retail Store - Genius Bar
https://www.apple.com/retail/geniusbar/