If you do a google search for 'your motherboard model users guide', you might find other sites that you can download the manual from.
I'll figure you've tried hooking your speakers to all the connections on the back? If so, then you might have a bad driver. I recently setup a system and with the wrong audio driver, my audio out and mic in were switch, (never seen that before). I used the driver that came on the mtb CD and everthing went back to where it was supposed to be. If you've downloaded a newer audio driver, then try the one that came on your motherboard CD. If you installed the CD one, then look for the latest audio driver for the audio chipset your motherboard is using, (ie; realtek, etc, etc).
Double check your speakers on another system just to be safe, unless you know they're 'known Good'.
Post your exact motherboard brand and model number, and I'll see if I can find a user's guide for you. I can post the download page here , if I find one.
Check the volume settings also. Maybe you muted the volume or turned it down by accident. Can't hurt to double check that.
Wabbit