If there seems to be no power on going to the phones, check the outlet the phone system is plugged into. If the system is plugged into a battery backup/UPS, make sure it is turned on and that it is plugged into a working power outlet. Try to bypass the batter backup/UPS by plugging the phone system directly into the wall outlet. You may have a bad battery in the battery backup/UPS. To ensure the phone system is not at electrical risk, replace the battery backup/UPS as soon as possible.
If the phones and the phone system have power, try calling the telephone numbers that are connected to the phone system. If you get a busy signal or a service message from the service provider, contact your service provider. They can check the service remotely.
If you have power to the phone system and telephones, and hear ringing when you call your main telephone number, contact Bestcom for a tech to come on site. It could possibly a phone system issue or an issue with your carrier.