Optiplex sx280 Display

I hope that someone can help as I am at my whits end. My problem is as follows:-

My intention is to try to get my wife interested in using the computer, so I have put an sx280 in my kitchen for her to use.

I connect a monitor to it'BenQ'  start up the computer, and it works fine.

I remove the vga lead and connect to the Sony lcd  KDL20s3000 15pin vga port, select pc, and it works fine, resolution set to 1024x768, as well as many others

Switch off the computer and Sony ....Sony says no sync when I start pc ans sony again

Re-connect to Benq monitor...no sync

Switch off pc and monitor + restart, all ok.

I have updated all drivers from microsoft and dell...to no avail

I have tried to contact dell and sony technical, but I think that with the info you need to input to them its easier to hack the Whitehouse!!

My thoughts are that it may be a pin out configuration problem rather than a setting problem, as I have tried DVI- Hdmi lead and set display to digital.

Every setting on the display options also.

However, when I connect my laptop to my Sony, all is fine.

It seems very important that a standard vga monitor must be connected on start up, as there is no chance of starting up the sony pc screen from the pc.

I could I suppose have two monitors in my kitchen, but it looks naff, and I am sure that my problem is not unique.

I don't think that my problem is unique, but it sure soaks up time..........Please help someone!!!!!