A couple of possibilities.

Your router may have updated it’s firmware and settings have been changed. Check the following page to see if anything stands out.

https://support.sonos.com/en-gb/article/sonos-system-requirements

Or the Play:3 may have an issue with its wireless radio. Are you able to temporarily wire the Play:3 to your router to see if it connects that way?

If it does and you are then still unable to see it when you disconnect the Ethernet cable, I would wire it again, then contact Sonos Support to discuss.

thanks for your reply nothing has changed with my router I have connect through ethernet and all works fine but soon as I try to connect through wireless it does not connect i will have to contact sonos although its quite a few years old now