My screen randomly became unresponsive and I can not restart it because I can not use the screen or enter my password. Is there a way to fix this?

My phone was working fine until a couple hours ago. I did not drop it. The screen is not broken or cracked. It just stopped responding. I tried to turn it off but can't since it doesn't respond. I have plugged it into a computer but I can not enter my password on my phone so I can not restore it. What should I do to get it to work again?