DP 715 no dial tone



I have a DP 715 phone with one extension phone since I have two business lines. One phone works just fine and the other one had a call come in this morning. When I answered it, the phone went silent when I turned it on, with no dial tone. I cannot call out and calls made to this phone go straight to voicemail. I have tried re-booting the phone twice and I still cannot get a dial tone. I called Vonage and they said to press the round menu button on in the center at the top of the phone to access a menu. When I press it, I hear a short “beep” but the screen does not change. Is there a kind soul out there who has had this problem and knows an answer?