Windows 7 No Audio Output Device is isntalled

So..... what you are saying is that, as far as Windows 7 knows, there is no Sound / Audio device present, neither in nor on your computer.
Time to take a look at the system BIOS and see if there is anything in there that has any of the onboard devices disabled or off or whatever the negative not installed setting might be.

Can you explain how do i do this in details please?

It would sure be wonderful if I could but unfortunately I can't.
With the method of even entering into the BIOS Setup Utility so varied from Computer to Computer, Laptop to Laptop, Motherboard to Motherboard not to mention the method of navigation once you are inside, the method of changing settings once you find the one you are looking for. I could explain in detail how I would do it on my computer but that would likely be absolutely worthless to you. Heck it wouldn't even work on the other computers in my own home.
You'll need either the Documentation that came with your specific computer or else you'll have to search Google (good luck with those keywords) and see what you can find as it might apply to your specific instance.
All I can say with reasonable certainty is that most if not all have a means of disabling or turning off some if not all of the various integrated hardware devices and I suspect that if Windows doesn't see your device in device manager (even as a problem device) then I suspect that it is either turned off / disabled in the BIOS or is otherwise inoperable as in broken, or failed.

Some more Google'n specific to this issue shows you are not alone

http://h30434.www3.hp.com/t5/Notebo...ed-No-CD-DVD/m-p/723725/highlight/true#M13626

http://h30434.www3.hp.com/t5/Notebo...nstalled-NOT-A-SOFTWARE-OS-DRIVER/td-p/564641

One clever guy even booted to a Linux Live Distro CD to determine if it was actually a hardware issue or a Windows issue.

Did a bios reset, now i have under sound thing in device mgr the realtek driver but it is yellow

Right click it and choose properties, go to the details tab, change to hardware ids and copy and past those lines into your next post

hdaudio\func_01&ven_10ec&dev_0260

That should be this driver from here
http://www.realtek.com/downloads/do...=24&Level=4&Conn=3&DownTypeID=3&GetDown=false
Check the box that says "I Accept blah blah"
Click Next
Get the correct driver for your system architecture (32 or 64 bit).

Installed the link, restarted the pc, opened device manager and the Realtek thing is still yellow.

IF you right click the problem device.... what does it have to say specifically as to why it's a problem?

Windows cannot load the device driver for this hardware. The driver may be corrupted or missing. (Code 39)