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If it works in Safe mode, but not in normal mode then that means the issue is with the system files. I've some solutions that you can try.
Solution 1 :
First reset the PRAM (it is a temporary memory) of your Mac. Follow the steps below to reset the PRAM and NVRAM
Shut down your Mac
Restart and immediately hold down Command-Option-P-R keys at the same time
Hold the keys down until the computer restarts and you hear the startup sound for two or three times.
Release the keys and let the Mac boot up.
Solution 2 :
Turn off your Mac by holding down the Power button for 10 seconds to turn it off. Turn it back on and immediately hold down Command and R keys at the same time for 15 seconds and this will boot your Mac to the Mac OS X Utilities screen.
From there, click Disk Utility.Select your hard disk at left column (Macintosh HD or hard disk name). Then click Verify Disk (under First Aid). If asked to repair, click Repair Disk.Then click Repair Permission. Restart and check if it is working
If the above two options didn't work, then you have to reinstall the OS X. Reinstalling won't delete anything from the Mac, but replace corrupted system files with new one. However, I'd recommend to backup your important files to an external hard drive before reinstalling the OS X.
Restart your Mac and immediately hold down Command and R keys at the same time for 15 seconds and this will boot your Mac to the Mac OS X Utilities screen. From there, click Reinstall Mac OS X. Then follow the instructions to reinstall your Mac OS X.
(If that didn't work, then restart your Mac and immediately hold down Command, Option and R keys at the same time for 15 seconds and this will boot your Mac to installation screen. Follow the onscreen instructions to reinstall)
Please let me know if that didn't work, so we can continue troubleshooting.