DIAGNOSIS A solid white light means the Ray is powered on but not connected to your Sonos system. It's in a kind of limbo state, often after a power surge or network change.
FIX You need to force a reconnection. 1) Unplug the Ray from power. 2) While it's unplugged, press and hold the Play/Pause button on the top of the soundbar (it's the one with the two vertical lines). 3) Keep holding it and plug the power cord back in. Continue holding the button for about 5 seconds until the white light starts flashing rapidly. 4) Release the button. This forces the Ray into setup mode (flashing green light). Now open the Sonos app—it should prompt you to set up a new product. Follow the steps to reconnect it to your system.
IF THAT DIDN'T WORK If the light doesn't flash after the button hold, try a full factory reset. Unplug the Ray, then hold down the Connect button (the one that looks like a sideways figure-eight or infinity symbol) on top while plugging it back in. Keep holding until the light flashes orange and white. This erases all settings, and you'll have to set it up as a brand new device in the Sonos app.
HEADS UP This process won't delete your Sonos account or other speakers, just the Ray's connection info. You'll have to re-add it to your rooms and redo any Trueplay tuning if you use that.