Here's a few things you can try on your own to get your PBX back up and running.
- Is your account active?
- Reload your PBX or powercycle your SIP device.
- Ping the SIP proxy you're connected to - you should get a response.
- Verify your Internet connection.
- Verify you have power.
- If you're using NAT, verify your port settings.
- Verify your Trunk and Registration settings.
- Check how you're telling us to route your calls.