My modem hangs up after connecting

[Edorch]

I have 2 PCs running Win98 and an external US Robotics Sportster Flash modem.
The PCs have different versions of Win98
They have identical drivers and identical settings.
The same external modem and cable is used on both PCs
One PC connects fine every time
The other PC dials the ISP, connects and then hangs up
I have tried different ISPs and most combinations of settings

From the Log:
Recv: <cr><lf>CONNECT 19200/ARQ/V34/LAPM/V42BIS<cr><lf>
Interpreted response: Connect
Connection established at 19200bps.
Error-control on.
Data compression on.
Hanging up the modem.
Hardware hangup by lowering DTR.
Recv: <cr><lf>NO CARRIER<cr><lf>
Interpreted response: No Carrier
Send: ATH<cr>
Recv: <cr><lf>OK<cr><lf>
Interpreted response: Ok

etc

1. Which end is causing the disconnect?
2. How can I prevent it?