In response to the suggestion that I look at the mixer. Firefox Plugin Container is not one of the sliders in the mixer. Also, the sound problem is the same in IE9 and IE8, and Chrome as well.
In response to the question about the sound cards, I should clarify that I installed 2 sound cards after disabling the onboard sound card, but only one at a time. At no time was more than 1 PCI sound card installed at one time. The onboard sound card is still disabled.
I also tried to let Windows find a 64 bit driver
for the onboard sound card, but this failed.
Seavixen suggested looking at the BIOS, but I don't know what else to look for other than having the onboard sound card DISABLED.
Thanks for all the suggestions, and I'm still open for more suggestions.