You can go into the WiFi settings and verify the password, or change it to something new to see if that works.
Go to http://192.168.0.1/#!/usage , click on WiFi Settings, enter admin as the password, and then verify the password for the 5GHz radio, or change it to something new. The password should be the same for both the 2.4GHz and 5GHz radios by default, but it's possible they are different.
Keep in mind that some things may not be able to utilize the 5GHz band, even if they can "see" it.
