Dell D800 won't boot up

I've got a Dell D800 Latitude laptop and it won't boot up. It tries for about 5 seconds and then nothing. The lights stay on but the hard drive stops and there is no screen. I can hear the fan running. I did a LCD check by hooking up an external monitor and toggling between it and the LCD display, and got nothing on either one so it's not the monitor. I checked the memory sticks, so it's not that. Could it be the CPU or the motherboard? I did some test on it where it beeps once then pauses, beeps 4 times, pauses and then beeps once more, but I have no idea what it means because it gives a code on the screen for you to reference it on a website, but my screen doesn't work. Does someone know what the beeps mean or do you have some advice on other things I can check? Thanks for your help- because Dell is absolutely NO help!
(((((((Dannydmode)))))))

The beeps mean different things for different mother boards. You have to search the beep codes for that mother board.