Windows 7 upgrades rarely get this right. But please tell the forum how you know the drivers are correct and up to date. And let's lead off by the Driver Update button in Windows is not assured to work. Tell the forum more.
I recently upgraded to Windows 7 on my gateway laptop from Vista. When I hook the computer up to the HDTV using an HDMI cord the picture looks great but the audio comes out of the computer. One of the biggest issues I have is under the playback tab in the sounds menu it says "Nvidia high definition audio not plugged in" under HDMI audio output. All of my drivers are up to date and I have been yet to find a solution to this. From what I have read this is a fairly common problem.