Hp pavilion dv4000 screen wont turn on

while its off try holding down the function key and the microsoft key and the B button and press the power button and hold all of them down for 5 secs that will get u into the bios look around in there be careful set it for default settings maybe even test battery in bios thats just 1 thing the next step would require a couple small purchases to eliminate the easy things let me know if you want also take out you cd drive gently while laptop is off all the way off not hibernate let me knowl

load the recovery CD and reboot run boot on cd

Hi, you can do a hard rest by following these steps:

Turn off the pc
Remove the cables and the battery on the laptop
Press & hold the power button for 5 seconds
Reinsert the battery and cables to it
Turn on the pc

that is how to do a hard reset....

download the ultimate boot cd and test your hard drive.

http://www.ultimatebootcd.com/download.html

I have the same model with the same symptoms in for repair. This is a motherboard issue and requires a reflow of the GPU and chipset. It has nothing to do with the LCD because the buttons don't react when the laptop is "turned on". The touchpad turn on/off button does not react when pressed, the same is with the wifi, volume and mute buttons.
The problem is in a poor solder and a cracked/oxidized contacts due to heat buildup.

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Try to re-install your audio drive. Before you do that you must first uninstall the previous audio driver installed on your machine. If you don't have the installation cd you can download the driver from HP site (www.hp.com/support), just click drivers and downloads then key in your machine model and look for the audio driver.

Have you tried F8 instead?

It is possible that the file Lsass.exe has become damaged or is not properly linked to the other files in the security system. Reset this file by using the following steps:

1. Turn on the PC and press the F8 key repeatedly when the first screen appears.
The Windows advanced options menu appears.
2. Use the Up and Down Arrow and Enter keys to select Return to OS choices .
3. Select Microsoft Windows Recovery Console .
NOTE: If "Microsoft Windows XP Recovery Console" is not listed, restart the PC with a Windows XP CD, Recovery Console CD, or Recovery Tools CD in the top CD or DVD drive and open Microsoft Windows Recovery Console. If a Windows XP Setup screen appears when using Recovery Console CDs, press the R key to open the Recovery Console.
NOTE: If "Microsoft Windows XP Recovery Console" does not list and you do not have a CD with recovery console, try the following:
a. Turn on the PC, and press the F10 key repeatedly at the first screen.
b. At the Recovery screen, click Advanced Options .
c. Press the Alt + D keys at the same time to open a command prompt window and skip to step 5.
4. When the login prompt appears, press the number next to the windows version (minint or Windows) and type the logon password. Try pressing Enter if you do not know the password.
5. At the command prompt, type the following: diskpart
6. Press Enter , do one the following:

• If a table of volume names appears, remember the drive letter next to the main drive volume name (usually D or H next to HP_PAVILION or PRESARIO) and press the Esc key.
• If a diskpart prompt appears, type list volume , press Enter , remember the drive letter next to the main drive volume name (usually D or H next to HP_PAVILION or PRESARIO), type exit when done, and then press Enter .

NOTE: If the main drive volume name does not appear in the list, the PC needs to be recovered.

This will show you how

http://h10032.www1.hp.com/ctg/Manual/c00530488.pdf