Odd. Usually, when you set up a Beam for the first time, it requires you to attach it to a Sonos account. Any chance you bought it used? If so, the previous owner may not have reset it properly. 

Under the assumption that you have other Sonos speakers in your system, go ahead and factory reset it. When you go through the set up process again, it will force you to register it to your account, so it will show up on the www.sonos.com list.

However, if it still shows up there, but isn’t showing up in your controller, do not factory reset it. Instead, wire it temporarily with an Ethernet cable, then try a simple power cycle. And if that doesn’t work, call Sonos Support directly to discuss it.