A couple things you can check quickly
The lights on the ATA device are on and solid, specifically the Power, Ethernet, and Line1 indicators.
If the Ethernet light is out, that means that there is likely a connection problem between the device and your internet connection. This includes intermediate devices like cables, Switches, routers and Internet modems.
Also be sure your phone is attached to the Line1 connector on the device.
Please check all of these, and that all the connections are correct.
The first thing that should be done is to power cycle your device, this can be done by simply unplugging the device, waiting about 10 seconds then plugging it back in.
If the device comes back on line,
Still No dialtone, the Power and Ethernet lights are on and solid. Now what ?
Verify that your Internet connection is working properly, by simply using your computer to browse to a website.
If all these fail call us for additional support