Ok, I may be a bit late to the party but I have to chip in here.

The reason you are not being allowed by your computer to reinstall Windows is because the disk you have is old. Stating what you already know, I know, but there is a reason.

Microsoft stopped supporting older versions of Windows XP. The version you have on disk is one of the older, unsupported versions.

In order to get security and critical updates, you must have a minimum of what's called, 'Service Pack 2' usually abbreviated to SP2 - this is one a range of updates rolled out by Microsoft since the development of Windows XP.

Your computer, over time, will have gradually been updated - the first major update to Windows XP was Service Pack 1 (SP1). For a long time, a person could update their computer from a very early version of XP, then Microsoft would only allow critical updates for users who had SP1 installed. This went on for a time until we get to the current stage where only SP2 is supported.

This all works fine if you have kept your computer updated and do not have the early version of XP.

If unfortunately, you try to install from a very early version, your computer will not get updates. So, it is not a good idea to format the HD or remove Windows XP from your system.

To your original problem with the dialup ... often, when you phone up these helplines they tell you any old nonsense just to get you off the phone; 'reinstall the ISP software' reinstall Windows, reinstall the chair you're sitting on, whatever. Don't fall for it.

They have a limited time to deal with customers and they MUST deal with them within that time. If they fail to do so it means their performance is slipping, ergo, they want you off the phone so they will tell you any old rubbish about reinstalling whatever because they know it will take hours to do it and they will probably be finished their shift by the time you get back on the phone.