1. Please check the cable connection between IP phone and handset.
2. Replace the cable used to connect IP phone and handset with a new one.
(If you don't have another cable, bring the old cable to a telephone / computer store and show them, they can help).
3. If you can't hear dial tone from handset, try to press "SPEAKER" button on the phone, to see if you can hear the dial tone. Please also check the connection cable between handset and the phone.
4. Try a higher volume setting.
5. Try solutions of last scenario.
6. Contact your dealer if above solutions don't work.