There are a few possibilities why you lost dial tone. Here is a checklist of things you can check.
1. Make sure your
internet is working. If you internet is not working your phone will not
work because VoIP requires high speed internet in order to work.
2. Make sure the
telephone is plugged into the appropriate port, Phone 1 or Phone 2.
3. Disconnect and
re-connect the telephone cable between the adapter and telephone.
4. Power cycle your
phone adapter by unplugging the power wait for 1 minute and plug the
power back into the adapter.