Issue: Computer is booting in Safe Mode (Shift Key) only

Do a Diagnostics Test (D) to check computer hardware

ref link

• Shutdown. Power on and immediately press D. It’ll take a few minutes to run tests and give you results.
• Mine gave me The battery requires service Reference Code: PPT004
• It’ll also give you your Mac’s serial number. Mine is: C02KTD35F5V7

Check System Diagnostics Log file

See link 1, link 2, and link 3

Reset PRAM Boot arguments

ref link

• Power on and immidately press Cmd+Alt+P+R. Release the keys once the system has reset and sounds the boot chime again.
• This didn’t work for me

Reinstall OS X

this might work if third party kexts are being loaded and causing the issue

Check hard disk

• if you’re able to boot in safe mode, open Disk Utility and Verify Disk.
• (Optional) Verify Disk Permissions and repair permissions.
• My hard disk was OK