MacBook Air won't restart on its own.

Hello! My MacBook Air will not restart on its own - I have to hold down the power button for the computer to restart. This happens even when I try to update the computer and a restart is required. I have let the computer prepare to restart for up to 30 minutes without any progress. This is the only problem I've had with the computer since I got it about 4 years ago and the current problem has been going on for 1-2 years. Thanks in advance for any advice!