Have the speakers never worked? If they have worked in the past, you could try a system restore to a time when they did work.
Natch you need to be aware of what you and/or microsoft have done to the machine since that time.
My daughter's lappy has a habit of removing recognition of the in-built speakers when she connects external ones via USB port, (for skype headphones) rather than via spkr out. As I'm not competent enough to figure out why, I tend to use system restore.