Please help, pecuiliar VGA problem

Hi,

I am having an average Nvidia 8400 GS as videos card.
For 2-3 weeks I did not have any problem with it. But strangely 1 day I see that my monitor is showing no -display.I switched on my monitor to the OnBoard Intel GMA adapter and it started woking fine. I thought that the problem is with the GPU card. so I took it to the vendor ( it is under warranty ). But strangely the shop owner connected the GPU card through the VGA port and and concluded that I have monitor problem , The card is fine.
Now after coming back I connected the GPU card through its S- Video port to a CRT TV .and I could see that the card is working.

So guys after patiently reading through this What do you say.Long story short.

The Vga connector of my GPU chip do not work particularly with my monitor, But the monitor works with nthe onboard graphics
Please respond folks.

Yes it can be mentioned that my VGA cord is an old one ( it do not have 15 pins) it has 13 pins
Regards