I have Windows 7, sp1, and have had this issue basically for as long as I've had my computer. Went with the onboard Realtek audio figuring I wouldn't need anything else. For the last 18 months I've looked high and low for an answer, never found my particular problem online and none of the solutions offered to other close problems worked. Here's the jist of the problem:
Completely randomly and out of the blue, my sound card will stop functioning. When I either reset my PC or put it into Sleep and bring it back out, the sound resumes. This comes with a number of weird anomalies. First, my microphone still works, so I can communicate to people that my sound has died. Two, the sound playing still shows up in my speaker levels as if it were working but nothing comes out. If I'm streaming my computer although my microphone still works my sound stutters at atrocious levels. It used to only happen once in a blue moon, or once or twice in a given week then not again for another month, so I'd research the answer for like 30 minutes after getting really upset then forget about it and move on. Over the last 2-3 weeks it's been happening with increased frequency, though it still just happens completely randomly. I'm hoping to once and for all fix this problem.
Fixes I've tried:
1) Uninstalling old drivers and re-installing the latest ones.
2) Checking Event Viewer for conflicts
3) Tried killing and restarting the audio services process (can't remember that one off the top of my head)
4) Tried disabling and re-enabling the sound output
5) Tried multiple headsets of different brands plugged into both sets of jacks
6) Cleaned out my computer
From reading a ton online it sounds like I most likely have a conflict, not a hardware issue, but how to figure out what's conflict if at all (since Event Viewer shows nothing) I have absolutely no idea.
Kinda frustrating I've got no response so far but I've found out something else interesting. Occasionally I can fix the problem by disabling and enabling my speakers in the Playback Devices window. Rarely, the first time doesn't fix it but the second/third time does, and probably half the time none of it works and I'm stuck hibernating/starting again.
I've tried that with new drivers periodically for the last year or so. That's never fixed it. I'll probably just give up and buy a new sound card since that's basically what Realtek suggested to me via e-mail once they decided it wasn't a driver problem.
What brand MoBo? I've had the same issue with my Gigabyte, and like yours, it's been sporadic enough that it's frustating, but hasn't justified a significant effort to fix it. I'm experience everything you described -- random fails - reboot always brings it back. I hadn't thought to try disable/re-enabling the speakers -- I'll give that a try.
Thanks for the tip about disabling and then enabling the speakers.
I've suddenly been having this issue too and that seems to fix it.
I just had the same problem but I opened the realtek HD manager and then the advanced settings tab. The first check box was checked. Under Playback device the first check box " mute rear speakers when a front headphone is plugged in" was checked. I clicked the second box and all works again. I don't know what changed it but I had to do this once before and no there isn't a headpone plugged in on my system.