Seems its onboard sound, so, go to bios and enable your sound card.
If it is enabled, disable it, loads in to windows, give it a few mins, turn off, enable in bios again, and load bios defaults.
If it makes no difference, as you got a compaq, Pc:
Go to the following link:
http://h10025.www1.hp.com/ewfrf/wc/s...c c=uk&os=228
Download drivers, and flash your bios also.
Should then work for you.