I have a Dell E6420 that will not boot. When I press the power button, the fan spins up for for about 3 seconds and then stops. No LED diagnostics lights appear. I've taken out the HD and reloaded it in another laptop and booted it successfully so the HD and OS should be fine. I've tested without the battery installed and only power adapter connected. I also verified that the power adapter is working fine. I opened it up and took out and re=seated the RAM and verified the fan is in good working order. Any other ideas?