My Roam had been plugged in but unused for several months (it is in a vacation house that I visit only periodically). When I attempted to use it, it would not turn on. I scanned this forum and found many others in the same boat and saw suggestions for attempting to get the Roam to work - none of them worked. 

I initiated a chat with Sonos Tech Support (note: phone wait was over 90 minutes and I was 30th in line for chat attention, but I hung in there). The very helpful technician had me go through the troubleshooting steps (12 second power button, 5 second power button and play button) but nothing worked. Sonos will replace my Roam with a Roam 2.

The technician strongly recommended that when a Roam is not going to be used for an extended period of time, it should be disconnected from the power (either USB-C or wireless). While it is unclear what an extended period of time means, I’ll try this with my new Roam 2.

I hope this works for me and other Roam/Roam 2 owners.