Have you tried to do a BIOS recovery ??
Do you have a different graphics card you can try?
Thanks for your replies. My pc is at the online shop (since 27 Sept) . I located the recovery program, using my daughter's old agp pc, which I sent to the store. They apparently tried the recovery without success. They also tried their own video (as I mentioned in my first post) and it worked, according to their feedback. My concern is how can my video suddenly become incompatible? To my mind I'm still caught between a rock and a hard place.
I can report that my new DP55WB is now working with the GT240 after the supplier tested a whole lot of different bios editions. In the end one was found that kicked the pc to life, it wasn't the orginal bios, but WB0142P.BIO. My only complaint now is a very much restricted bios choices compared to the original, but I can live with it. I hope Intel can straighten this out with a new edition (that works for me)