This is weird!
The modem (Compac Presario 336-VSC internal), hangs up unexpected in the middle of an initilization (negotiation between, 2 modem when dialing my ISP). Or rather at the end of the init before it sends login/password (so that's not the problem!). This is the case when I dial my ISP using a PPP connection.
When I then try to connect via Hyperterminal under w95, the same happens, but earlier in the init (half way through).
The phoneline seems to work ok.