I have one sound card onboard and other one, offboard, a AWE64. Both are installed in my Windows ME, but when start my Windows only the onboard work correctly. I need restart my computer to work both soundcards correctly.
Best thing to do is disable the onboard sound in the BIOS. You may also want to consider upgrading to a PCI sound card, depending on how old you computer is and the type of hardware you're running in it.
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