Go into your control panel, and instead of disabling the voicemail, enable it and set it for some high amount of rings. Set your answering machine for ring number below Voipo ring number. Verify that you have internet connection with your computer connected to same router. If you do, unplug power only from adapter and plug wait 10 seconds. Plug power back in.

BTW, I do believe that Voipo would have sent you another adapter with built in router, such as a HT-502 or 702. By default they send out adapter without built in router, but not everyone has a router.