Reset the router to it's default configuration, and then make sure you secure the admin access to the router in every possible way (change the password to a stronger one, allow only a certain system to access the admin setup of the router, etc). Also, set up a WPA secured access for your employees only, to separate them from the general un-encrypted access for customers.
Our business has an open wifi for customers to use. This morning when we tried to use it, and there was a password block on it. How do we re- gain control over it? Thank you a head of time. Rich
Simple enough; find your router and just hold down the necessary reset button (in the case of my linksys router, it's a large orange glowing Cisco Systems logo). If you have a hard time finding it then look on your manufacturer's website and they'll tell you. But basically holding it down until the LED turns off or changes color will disable all preset security measures.
If you have access to the Wireless Access Point (WAP), or Wireless Router, then Just Perform a System Default Reset, then, you'll just have to reconfigure the WAP to have the same SSID (Network Wireless Name) that it had before.
On a side Note, I'll recommend to have a password for the network though (or at least check if your WAP lets you put a password for accessing the configuration, most of them do), 'cause that problem will just keep on happening if you have an open Security on the Network
Also, once it is reset, verify that Remote Administration is turned OFF, and WiFi administration is turned OFF. It usually is off by default, but check just to make sure.
This will prevent anyone from changing the settings wirelessly. They'd have to be actually plugged in to one of the router ports.