[Asterisk-Users] incomingcall braking all

[Altus Snyman]

Good day all
We have a voicetronix openline4 card.Asterisk is configured for sip with
all the extensions and all&all.
I can call out and internally,to dial out I have to dial 0...
My problem is with incoming calls
If I call my external PSTN number,asterisk answers with the default
message and if I press the extension it goes to the right sip client.
BUT

As soon as I hangup this call all gets buggered!:
If I dial out it plays my answering message and when I try calling back
in it doesn't pick up it just rings.
Even if I'm in asterisk and do a STOP NOW it just freezes!
I have to do a kill -9
Can this be from my ISDN analog line or something
Please HElp
Thanks

Altus