He's only had the machine a couple of days so I'm not sure. Is there a generic website he could try?

Online banking is working fine. Am I right in thinking the downloaded .exe actually starts the download of the program from Microsoft?

Do you have any security software installed like Avast or Kaspersky?

He has a 30 day trail of Norton, but I don't know which one. However when the .exe is downloaded Norton says it's OK.

Not heard any bad reports of Norton in this respect so I think you're *probably* OK with that one.

As its getting a bit desperate now I'd try restarting the computer, and creating a new local user account with a password, and ensuring it is a "computer administrator", and attempt the install again.

You could dig into the event log but its easier to try the above first.

Thanks for the advice. Not being confident with computers I think he would probably opt to take it back to the supplier and get them to sort it. Would it be safe to disable Norton and try?

Yes, quite safe.