Modem dials then hangs up

I have a windows 95 system , new modem. The modem has tested OK. The system is on a 2 pc network direct cable via network cards.
When trying to connect to the internet the modem dials then immediatly the dial tone is heard again. I have listenedin on a phone attatched to the modem.
The modem has been tried using the system as a stand alone on a different line and it works ok?

Help appreciated