Troubleshooting

Why does the Prefix/Scoreboard not show up or the whole plugin does not work?

A reason because this may won't work is that you might have another Scoreboard Plugin installed. Other prefix plugins also count as scoreboard plugin because they also use scoreboards (scoreboard is not always the right board on your screen! They are used for a lot of other stuff too!)

To check which Plugin may cause the error, remove all Plugins from your server and then slowly add them again. Just add a few and then reload the server to check if the scoreboard still works. If not, then the last plugin that you added back to your server causes the error. Then there are only two options:

1. Contact the dev of the other plugin and ask if they can fix it (probably not because of the way MC works)
2. Remove the plugin or find a similar one.

If you removed all Plugins from your Server but it still doesn't work, then you should check if the Plugin is correctly configured and installed. To check if there is a wrong setting, rename the PowerBoard folder to something else and restart (no reload) the Server. A new folder with the default settings will be created. If the Plugin still does not work with the default settings and no other Plugins on the Server, check your Server Software and maybe update to a newer one.

It is only confirmed that the Plugin will work with Spigot and PaperSpigot. Please also make sure you have an supported Minecraft version.

The player xy has no Rank! Make sure that he has the correct permissions.

It is exactly that what the error message says. The player has no rank, so you have to give him one. You should set a default rank to solve this problem for new players. Every permission system should have a default group. You can give this group the permission for the rank.