Well, nobody has written anything in this forum in quite some time, but I've made a bit of progress in this realm, so I thought I'd post it. I had this same issue and went bonkers trying to fix it for hours. I tried drivers, bios settings, system settings, default sound devices, even looked at the motherboard thinking I might see a frayed lead or broken solder point or something, but nothing worked. Finally I just started clicking on things, and found a setting that doesn't FIX the situation, but allows you to get sound again.
Here's my take on the situation. Your computer has (had) the ability to watch your jacks and determine when something has been inserted into them. The Realtek HD Audio Manager uses that input to inform you (quite helpfully?) that you have just inserted or removed something from an audio jack. It also uses this information to determine which devices you're using, and to limit your options when it comes to settings and control panel tabs, apparently so as not to confuse you by allowing you to make changes to device profiles that aren't currently plugged into your computer.
Here's the issue, this functionality likely relies on the detection of very small amounts of electricity being run through the jack...the plug completes a small circuit that signals the motherboard that something has been inserted...which is fine unless a larger jolt of electricity makes its way to that sensitive detector and fries the thing out. I can't guarantee that this is what's happening, but it makes sense. Anyway, now that your computer can't detect input changes, it also assumes you don't have anything plugged in, ever again.
In the past, again, this would be no problem...headphone jacks are just simple metal to metal to connections, so as long as nobody tried to get fancy with the software, you'd be fine, but wait, they did. In this age of wonder, if that very fragile piece of technology goes bad (mine lasted about a year, the same length of my Dell warranty) the Realtek software basically shuts down your jacks. There really isn't a fix for the detection as far as I can tell, not without replacing your sound card or motherboard. However, Realtek doesn't have to check the detection status to just play sound through the darn device, but they sort of hide the option. In the realtek audio manager (mine shows up in the system tray as a little orange speaker icon) there is an unlabeled icon that looks like a folder. It doesn't even look like something you should be able to click on, and what the heck does a folder have anything to do with sound, your audio devices, or front panel jack detection? Nothing, that's what. You'd never know that if you click on it, there is a single checkbox option within to "Disable Front Panel Jack Detection", but there is. Go in there, check the box, and Realtek will no longer rely on this broken detector to populate your Microphone and Speaker panel tabs, and you'll be able to get sound again. I know some of this was hinted at in other posts, but there it is. I hope this will save SOMEONE, SOMEWHERE, the anguish of smashing their head against their tower for half a day, but if not, I still feel better