Modem will not connect

I am unable to dialup to the internet. The computer opens the port, tries to dial then displays the error message:
"Disconnected... Error 628: The connection was terminated by the remote computer before it could be completed".

I have checked in Modem properties and the modem diagnostic query is successful with no errors reported. There are no exclamation marks in Hardware Device Manager and everything is reported as enabled and working.

The log file in Modem properties reports:
"Opening the modem device failed with error 00000020".

I am at a loss as to what to do now. I don't have access to the modem drivers so am hesitant to remove the modem from Device Manager and reinstall it because the drivers on the web are older and sound a bit flaky.

Running Windows XP Home and the modem is a HSP56 MR by PCtel.

Any ideas please?

 

Yes, the modem was working until recently. The computer has had a few problems which resulted in a reinstall of Windows, which then caused a problem with the dialup options being unable to be accessed until SP1 was installed.

I have just disabled the internal modem and connected an external modem which has worked and has connected to internet OK. Maybe the internal modem is stuffed?