I would try to use the service tag or the model number to get a spec sheet off the web. In many cases it will list the exact model of the sound card which is the info you need to know when trying to locate a driver. The driver more than likely is for an embedded sound device that is wired right to the main board. Use this information to find the driver and then install it.
Sometimes the service tag and the OEM's support website can tell you the exact configuration that system shipped with. If this is the case... You are golden as this is truly paydirt for this problem.
Based on an initial search this link looks like it might be the right location to get the drivers for that system.
M2000 Notebook PC Drivers Page
If those drivers do not work, then your laptop is a different variant in the M2000 line. You will need to look at the stickers on it and the markings to determine which specific variant it is. The page below will help if you make it this far with this problem.
Compaq M2000 Variant Listing