Hi:
Before getting into more detailed troubleshooting, here are some preliminary questions:
Is Google Voice the only service you have on this phone? If so, how many SPs are configured with Google Voice numbers? If not, do you have one or more SIP VoIP service providers configured? If so, do they have green LEDs and do they work?
Next:
If you only have one SPx configured on the phone, and it's failing, then:
Sign into your Google account (Gmail user ID/PW) on a laptop/desktop web browser and go here:
https://voice.google.com/settingsAre you able to see your Google Voice inbound phone number on that page, at the top of the page, to the right of "Google Voice number"? If not, do you receive any error messages when you go to that page? What does it say?
If your Google Voice number is listed at the top of the page, then look at the "Linked numbers" section. Ensure that you do not have any old, abandoned phone numbers listed. If so, delete them now. Ensure that you have at least one standard 10-digit US forwarding phone number linked. If not, add one.
Call your Google Voice phone number from some other phone number, NOT one of your linked numbers. What happens, in detail? The expected behavior is that the linked number will ring, and you can answer the call on the linked phone.