Odd, I don’t recall a case where you couldn’t perform a factory reset. I think that suggests some sort of hardware (or power?) failure, your best bet would be to call Sonos Support directly to discuss it.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Thanks for your reply - I’ll try ringing the support line . I think I made a mess of the reset and now it’s stuck - it won’t switch back on ! Help !