I have a problem with this my laptop HP pavilion ze4900. when i power it on, it doesn't boot up although light is on indicating that it is getting power through the battery or AC Adapter. i tried to change the RAM, nothing helps. Anyone has an idea how to solve this problem?

Try this sequence of steps

Remove any attached devices (usb etc)
Remove both the Battery and the Power Adaptor
Hold down the ON button on the laptop for 30 secs (this will disperse all internal voltage)
Put the Power Adaptor in only (ie leave the battery out)
Try turning on

If it works
Turn it off, and put the Battery back in
Turn it back on

Are you certain the hard drive is good?
Usually in that model, it is the lcd screen inverter or the hard drive. A failed inverter will make the screen remain black.
Hook up an external monitor and see what you get there.
Also try a cold boot in SAFE MODE, by pressing the <F8> repeatedly once per second as soon as you press the on button. That will sometimes bypass some of the screen, driver, and graphics problems but at a very low resolution.

Raybay, are posting in the correct thread?
Or are you saying that the laptop could in fact be booting up, but screen is black?
From my thoughts to the original post, the laptop is not posting

Not exactly. We have seen some fairly new versions of that model come in with a black screen, making them think it was not booting, when it was booting to a non-working Black screen... but the usual problem is that it was not booting at all due to a defective hard drive, and the laptop is dead except for the light.
I was merely suggesting that he take a closer look via those methods.
Hard to know what the user is actually seeing, but the power problem is usually not it..

Ok so if the user (on this laptop) removes the HardDrive, and installs an external monitor, we would expect to see the power on self test screen, under this condition. (possibly)

Worth a go

No. He or she may need to discover if either is the cause. But dealing with the hard drive and dealing with the inverter or screen are two separate issues. Of course I wouldn't recommend testing the inverter and screen without the hard drive.

Ok I understand that, actually we're on 2 to the power of 3 at the moment, of different hardware configurations

Try External monitor
Try HardDrive out
Try release all power
And combinations thereof

Can be Inverter; HardDrive; Power (that's my little bit); and after that...

mood please reply back with results.

typical problems for these laptops are: broken BIOS ROM image, burned ethernet chip.

Well, perhaps not "typical" but possible, as perhaps that sometimes, but rarely, does happen.... Tjat would be considered a failed motherboard and reported that way. The usual fix would be to replace the board.
Kimsland, I suspect, is looking for ways to fix common causes to the owner doesn't pay the $85 shop fee for something that can be done at home.

raybay, typical problem means in my way, that i repaired 10-15 laptops with same problem. i think this will be enough to say that this is typical problem for this series.

You're right, as you're aware, 99% of all faults can be fixed in 5mins (umm tech on site!)

I would say that you would know then. Even after 3 or 4 I'd say it's looks to be common!

Thank-you for your information (possibility). Please continue to help, with your knowledge and experience. (always on a high level in these areas)

Thanks to kimsland,raybay,lamo for trying to help me out. I tried to follow what u suggested but i couldn't succeed. The hard Disk of this Laptop works.
lamo you said that typical problems for these laptops are: broken BIOS ROM image, burned ethernet chip, how can i repaire these problems? IS it possible to repaire them without replacing a motherboard? If it is, how?

mood, you can unsolder bios chip and reflash it. when you unsolder the chip, post here a message, i'll tell you what to do. but there's option, when BIOS chip sits in the "panel", in this case, you can use PLCC32 extractor tool to put it out. anyway, when you'll hold the chip in your hand, post here the massage

sorry, i've forgot another otpion. there's possibility to reflash BIOS without unsoldering chip.you need the crisis disk for this laptop.
1. disconnect AC adaptor and battery(this is imortant!)
2. hit Fn+B
3. turn on laptop with crisis disk inserted(it's floppy disk ) WITH pressed Fn+B.

and tell me EXACT notebook partnumber.

Thanks lamo for showing good will to help me solving out this problem with my Laptop.

Where can i get this Crisis disk, can i download from the net? if yes give me the link. lamo Do you have yahoo email ID? if yes add me, my ID is mood48 so that we can chat.

The exact partnumber of this laptop is P J929EA#ABD

ok. you need floppy drive(internal or USB). the file in winimage format. download winimage and write floppy-disk.
here's the link:

http://www.sendspace.com/file/kisr5e