1. At the console of the ESXi host, press ALT+F1 to access the command shell.

  2. Enter unsupported in the console and hit enter. You will not see what you type.

  3. If you did it right you should see a fairly common linux command promt like: ~#

  4. Edit the file /etc/inetd.conf. Remove the # in front of the line that starts with # SSH.
    Do this simply by typing vi /etc/inetd.conf. Use the down arrow to locate the line.
    Press the letter x and save the file by pressing ESC once and then type :qw!

  5. Now, at next restart of the ESXi host you will be able to access the host via SSH.
    Or run /sbin/services.sh restart

Sources: vm-help.com & yellow-bricks.com