To be sure I repartitioned the drive and fully formatted it - then the install started. Mostly completed and then decided to constantly reboot, so it was back to square one. Eventually it was installed, then it was add in the drivers, service packs and updates. A few hours later I managed to get it all working, and the main applications I need installed (Sibelius, email, chat etc) I still need to get others installed, but its a good start.
Just after I had the updates installed there was a bang and the computer went dead. Sure enough the PSU had died. I suspose the stress of installing Windows was too much for it. I was able to take the one out of my server and use that. Its annoying now because I can't use the server, which is more annoying than critical. Having the server allows me to test stuff without killing one which is more critical (like, for instance, my works server). Looks like I'll have to add a new case to my list of parts.
One fact - with all the service packs/updates installed and a couple of other programs install the total install is around 6Gb. People wonder why I like unix so much - I can't even get close to 6Gb on Solaris if I install all bits of software I can - including all the extras (high level business applications and big database programs).