Can't receive incoming call from sip and iax

This is the first experience I had this program asterisk v 1.4.18 I had a problem in receiving calls from SIP and with IAX I hear the ringing but no sound after answer on calling . but i can make call
I have no panel for sip and iax , I do not know how the amendment from file editor .
pleas help me how can receive incoming call from anther SIP and IAX