It usually means it's lost its Wi-Fi connection or something else is wrong with the connection to the Internet, but I believe it could indicate some other issue. Roku has never made public any information about flashing lights that I've seen.
I’m having the same issue. I just opened my roku express HD its brand new from the box and I was trying to set it up and right as I plugged it in it started flashing a white light so I gave it a few minutes. I checked the connection and the cords and everything seems to be fine. I even try pushing the reset button and no luck. I’m not sure what is going on and making it not connect to my tv. Nothing has even showed up on my tv for any next steps. Any one know anything.
@ReannaLingle, have you ever connected anything to that particular HDMI input on your TV before (like a Blu-ray player) to verify the input is ok? Have you tried another HDMI input or another HDMI cable if you have one? Do you have another TV you can try it on? Are you using the supplied power adapter and not the TV's USB port? Have you cycled through all of the available inputs/sources using your TV's remote control?
If you've exhausted that list, take it back.
At least on the streambar, if you have wifi connected, a flashing white light just means the streambar is muted. Unmute it.