Why don't usernames appear above players in my game? (Short Question)

I don't think I have a script that disables it, how can i turn username visibility on?

Look in your explorer for a class named "StarterPlayer". The property responsible for name visibility is defined as "NameDisplayDistance". The default value for this is 100. If the value is still the default and names aren't appearing when you stand within 100 studs of a player, then it's likely that you have a script modifying it.