If the speakers have worked before then you should be able to get them working again, lets try the Aida route ( not used it my self, just saw it posted else where).
Launch Aida, Click the Plus (+) next to Computer,click on Summary, you will see lots there,hopefully Mutimedia \ Audio Adapter, hopefully it will have something in Value, if you hover over that with the mouse,it gives you the option to download, try that.Unfortunately the links don't always work, so make a note of what yours is, if the download doesn't tke you to somewhere that you can get it, post the information on this thread and I will see if I can fing it for you.
If it does find it, there will probably be a setup.exe, run that, re-boot PC and see what happens.
Steve