A friend of mine asked for my help since he didn't have any audio on his HP DV7 laptop. I tried several drivers but none of them worked. I came accross strange behaviors of his system too, and I'm pretty sure this is all relevant in this case.
First : they are 4 unknown devices detected in the devices manager, they all have this param : root\DTSoftBus01. I've seen that sometimes an issue is caused by Daemon Tools but he doesn't have it installed in this comp. He did have Virtual Clone Drive though, and I uninstalled it just in case. Nothing obviously happened.
Second : the audio drivers. It may be possible that the sound problem occured after an update for his geForce video card (updating HD audio in the same package).
The Device Manager state was this at that time : https://scontent-cdg2-1.xx.fbcdn.net/v/t35.0-12/13282543_1221784334507093_1203375319_o.png?oh=2371da5b15a9111e39a92cbb31821b77&oe=574CEAAC
Third : So I deleted all the drivers (audio and video) and unistalled the devices waiting for Windows to install drivers automatically with windows update. He actually found 2 (IDT HD Audio and Nvidia HD audio) but then I had issues with Windows Update itself (couldn't install those drivers nor install an optional KB from september 2015 : KB3080079)
So I did a sfcfix, chkdsk, checksur (couldn't terminate : scanhealth ok but restorehealth never worked). Did all the steps here (http://www.thewindowsclub.com/windows-updates-fail-to-install)
Thanks everybody for any help !