Inspiron 530 - Cannot connect to Internet

Hi

For reasons too boring to go into, I need to access the internet temporarily through my desktop PC via a mobile broadband dongle. the problem is that I cannot get a successful connection. I can open the ISPs application, it finds the network, but when I try to connect, I get an "unable to connect" error.  Unfortunately, the software is too basic to tell me why I couldn't connect.

I raised this with the ISP (Orange) and after trying various options, was told to try the dongle on another device. The dongle works fine on my partner's Optiplex. I moved my Inspiron next to her Optiplex, but still had no luck.  As far as the ISP is concerned, there's nothing wrong with the dongle, so there must be some issue with the configuration of the Inspiron that is causing the problem, but I haven't the slightest idea where to begin with this one.

The Optiplex is running Windows XP, while the Inspiron is running Windows 7.

I have unstalled and re-installed the mobile broadband launcher application several times.

I have not had any recent (e.g. within the last 3 years) known malware/virus activity.

Any assistance would be appreciated.

Paul