Latitude D610 will not turn on

Hi all

Help

My Latitude D610 suddenly froze and now will not restart.

Pressing the on button it make some noise, hard drive? and three lights come on and the 2 to 3 second later it shuts down.

I have re-seated the memory, have changed the fan, tried without the battery and from the docking station but always the same.

thanks in advance

malc