No audio/sound output from this compaq presario laptop despite having installed realtek audio driver and HD driver? what might be the problem

Well as you mentioned that you have already tried installing the driver then also the issue persists then it might be either a problem with the service responsible for the sound to work or the sound card .

In order to check that the sound card installed on the system is working perfectly we need to perform certain steps.

1.Restart the system and tap on the F10 key for while till we get to the BIOS SET UP UTILITY.

2.As soon as we get to the Set up Utility try tapping on any keys on the keyboard it would give BEEP sound.

3.If we get the Beep sound then the sound card is working and its a problem with the Operating System and we need to perform a couple of more steps,if it does not beep then the sound card is bad and call up Hp to get it replaced or get in touch with a local store.

4.Now if the keys beep on the Bios screen then we need to perform a couple of more steps on the Windows to check the functionality..

5.Click on Start, in start search or run type SERVICES>MSC and then hit enter.

6.Locate a service which reads as WINDOWS AUDIO.

7.Right click on that service and click on properties.

8.Check the status of the service...if the service is already started then the STOP tab would be highlighted or vice-versa.

9.If the service is started stop it and then again restart it, and if the service is stopped start it..

10.Now in the middle of the screen we would see a start up type tab, there would be a drop down menu next to it.

11.The drop down should be set to Automatic

12.Click on APPLY and then OK.

13.Restart the computer and then try installing the Realtek Audio driver and check the functionality..

Hope this works
Regards
KEN