I would check
A) If it is enabled or not or
B) If the driver is installed properly.
Click
Start > Run > type "devmgmt.msc" (without the quotation) and check under Sound, video and game controllers - if there is a red cross then it has for some reason been disabled (unlikey). If it has a yellow question mark then it 9 times out of 10 means that they drivers need updating/re-installing.
To update the driver you will need to either run a Windows Update or visit the manufacturers website - here is the Audio Driver for your laptop -
http://h20000.www2.hp.com/bizsupport...tem=hb-18341-1
I hope this helps - let me know how you get on.