Windows 7 not detecting onboard sound at random

I recently bought a new rig, and things were just fine until a few days ago when I shut the PC down. When it restarted, Win7 said there was no sound card installed. The sound is integrated in the motherboard, and worked just fine an hour before. I tried the troubleshooter, searching for new hardware, everything I can find, and it won't detect the sound. So I took it back to the shop I bought it from. Naturally, they plugged it up & everything worked fine. I brought it home, set up, everything worked fine. The next shut-down and restart, Windows 7 says there is no sound card installed. HELP!

Windows 7 premium 64-bit
MSI NF750-G55 motherboard (integrated sound)
AMD Phenom II X4 970 processor

I would suggest you uninstall and reinstall your sound driver. This used to happen to me when I used to use windows xp, difference was, I never got that message. Let me know if that solves your issue.

Okay, I downloaded and installed all the latest drivers found at MSI & Realtek, still getting the same results. I couldn't figure out how to uninstall the drivers first, though; see below. But the downloads did their thing to no avail. The readme file said they uninstall first, reboot, and then install, but they went straight for the install.

I'm a newbie to 7 and am really finding it hard to get around in the system (the old axiom about old dogs & new tricks is quite true!). So bare with me if I'm poking around in all the wrong places. If I go under Control Panel - Hardware & Sound & click on the Sound tab, all it says is "No audio devices are installed", and all options are grayed out. Under the Owner-PC properties tab I see 4 entries for NVIDIA High Definition Audio, all which report functioning properly. Still, the x-ed out speaker icon remains in the tray saying No Audio Output Device is installed. Clicking that Icon does not help; troubleshooter can't find the problem.

I also ducked into BIOS setup just to make sure onboard sound hadn't been disabled somehow, but it was all hunky dory there.

Any other ideas?

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