Hi. Thanks for getting back to me. I have followed your advice and now recognise that I did not correctly report the problems yesterday.
In Windows 7, it is as I said before, PC Magnum loads and scans and then a screen appears which says that "PC Magnum is loading" and the program hangs. It does the same in Windows Safe Mode With Networking and I have checked and my firewall (Kaspersky Internet Security) is giving permission for PC Magnum to access the Internet.
In Windows XP Professional, the program will not install. It says that .Net is not installed. But Windows Update has instal