Further progress
Thanks again. From your earlier suggestion I now have a better understanding of what is happening. If I connect the monitor direct to pc it starts up ok, I can then connect it via the switch & it stays ok because it has started up with ther correct driver & resolution. I can put the pc to sleep & restart still ok. Switching between pc & xbox still ok.
If I start the pc with monitor via switch the pc cannot read the EDID from the monitor so starts up with the generic driver so the picture is of the wrong resolution & not so good quality. Can still switch between pc & xbox but pc display is poor.
The monitors resolution is 1600 900, the generic driver dosn't offer this resolution the best available is 1280x720. If the generic offered 1600x900 I think the system would work ok or if the EDID software overwrite was availaable as suggested in your paper that would be the best.
Hope this is of interest to you - thanks for getting me this far. T