When I startup my windows 8 pro pc, my account which is an administrator displays whereas there is no back arrow for going back to other users login page. I have two more users which I can't see.

Were there any changes made on the computer prior to the issue?

The issue might have occurred if some third party application messed up the system settings. Follow these steps to resolve the issue and check if it works:

a. Press Windows key + R on the keyboard.
b. Type “secpol.msc” without quotes and press Enter.
c. On the left pane, expand Local Policies and click on Security Options.
d. On the right pane, scroll down and find the Interactive Logon: Do not display last user name.
e. Double click on it and click on Disabled under Local Security Setting tab.
f. Click on OK and restart the computer.

The option can be enabled so that you can improve security by hiding the user name of the last user to log on. Instead, users will need to know a valid account name for the computer.