My laptop won't boot

Hello,
My laptop won't boot at all whatsoever It will turn on but nothing appears on the screen the disk drive and cd drive will run but the only lights on are the power lights even when charging, I've tried swapping out 3 different hardrives and removing the ram but nothing prevails. I have tried it on an external monitor still nothing HELP
(P.S. I have removed the cmos battery cause it was dead but it ran perfectly for a week afteward till i tried to return the dead battery)