what you can try first is to unplug anything unpluggable:
power supply, battery, pcmcia cards, usb devices, firewire devices, anything attached to the laptop
if you can also remove the memory bars.
once done hold the power on button for like 30 seconds. dell calls that a hardware reset (at least they told us here).
done that just plug in the power supply again, try to switch it on and see if something happens.