Yeah...quite strange... Have you tried doing a system restore or windows recovery? If two sound cards give you problems, I guess it's just software. I guess it could still be hardware(as in your mobo dying) but it seems some PCI sound card would work rather independent of the motherboard...
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Primary- i7 920 | 6GB RAM | 9800GT | 160+160+500GB
Secondary- Athlon X2 4200 | 2GB RAM | 7600GT | 80+250GB
Netbook - Atom N280 | 2GB RAM | GMA945| 160GB
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