Firstly you should be reading AC voltage not DC. Ring voltage is based on Alternating Current not Direct Current. So, double check your power supply, it should be the 12VAC 500mA power supply that was provided by Channel Vision with the unit. Next look at the dip switch settings. There are two dip switches, one labeled CO/NO CO and another to select your command key for * or #. Make sure if you have an active phone line that the dipswitch is flipped over to CO. NO CO is if you do not have an active phone line. Please make sure that the phone line being provided is coming out of an analog output from the modem. It should be using a standard RJ-11 phone jack connection. Lastly if you have a test phone or butt set please connect this to the unit in place of the phones. The P-0921 does have a REN (Ring Equivalency Number) maximum and if exceeded could be causing issues. By using a test phone/butt set you can take the phones out of the equation. If you run through the provided troubleshooting and still experience an issue please contact Channel Vision directly for further assistance.