I got the same problem on my netbook after the security patches that came tonight putting it in sleep mode and waking it up made the sound return
Your link clearly shows you have Nvidia HD Audio, not Realtek or Via. Are you using Nvidia drivers? If not, that's the problem.
Download everest and check what device it really is, if you use wrong drivers then the sound card will not work correctly.
Everest shows: Code: Motherboard NameUnknown High Definition Audio Controller [10DE-055C] [NoDB]PCI BrookTree Bt878 Video Capture Device - Audio SectionPCI Nevermind... Win7 caused me so much trouble so I'm going back to xp/ubuntu.
Yeah, it's def a nvidia device. Some of the drivers that worked with XP won;t work on Win 7, so you might have to find a nvidia driver that is modified already. You can try looking on guru3d.com
Check whether your windows audio service is running when you are not getting any sound. On a side note, I had a similar problem with FRAPS on XP. If I shutdown without manually closing fraps first, then upon reboot I wouldnt get any sound. I had to uninstall the device from device manager then scan for new hardware to make it work. Maybe you have a similar problem. Also have a look at the event logs as they might show something.