Does Win7 install to another drive connected to the same controller port?
If it did, you could image copy it to the SSD and see if it can boot then, even if only to see if it works. There should be some tips around for doing the image copying, like using the latest Acronis True Image.
Thank you very much for your help.
The same problem with a spare 80 GB harddisk.
I replaced the video card, and everything is working fine now.