Your server was rebooted. Users have complained that the server refuses secured connections.
What is the mostly likely cause?

A.
The public keys have been corrupted on the server.

B.
The clients are not resolving the server name properly.

C.
Sshd is not configured to start in the default runlevel.

D.
The users need to ssh-keygen.

Explanation:
To enable the ssh connection sshd service should start. Probably on first reboot sshd service is not started. So you should start the sshd service.
To start sshd service service sshd start
To start sshd service automatically on next reboot chkconfig sshd on