Latitude 820 power up issue

I have a Latitude 820 laptop which has decided not to power up. The battery is fully charged (all green lights come on when test button is pressed).

When I plug the power adapter brick into the wall scocket the green light come s on on the brick. When i then plus the cord into the laptop the light on the brick goes out. 

When i press the power on switch on the laptop i get nothing.

I have gone through all of the steps in the Dell Fualt finding page even as far as taken out the memory cards and hard drive and battery and then putting them all back in to the proper sequence. But nothing.

Any ideas? Is there some kind of key sequence reset i could try? I did read on another post that with another dell laptop type to take put the battery and hold down power swtich for 30 seconds and then put the bat back in and try to power up. that did not help in this case.

thanks for any help comming.

Colin