I've had this problem off and on for a year or so, now it seems more constant. Sometimes my sound stops working on my laptop. No sound from speakers or my earplugs. I've restarted it a couple of times, still no luck. Also, Awhile back something happened where I hear a "white noise" sound at times(maybe when my sound IS working), and my fan(?) seems to be running constantly now. The drivers are up to date. I'm running Vista Home Premium 32 bit IDT High definition CODEC and High Definition Audio Device are mentioned in Sound category in Device Manager.
Well I know with my laptop the actual connector where the plug goes in was broken. Sometimes people connect earphones and they stick out, then set the laptop on their lap with the connection pointing out or resting on your leg. That puts pressure on the jack and breaks it. It usually doesn't completely stop working but rather when you move the connection around it comes in and out. If you have more then one jack I would try another jack but more then like that port is cracked if you look at it.