9.4 demo weirdness

Trying to install my 9.4 demo on w2k sp3, the server just kept refusing to start without giving any errors or anything in the log, whether I use starts or start it from Services. After a bit of digging I decided maybe the upgrade from 9.21 hadn't gone well and it would be best to unistall and start from scratch. But uninstall gets: "The product version of the installation program is not the same as installed version of the product or product is already uninstalled". Has anyone seen this before? What should I do? Alternatively is there any documentation to help check the quality of an installation? Many thanks Andy Kent