try the oldest trick in the book. uninstall ALL your sound card drivers. shutdown. remove the hardware. reboot. check and make sure the drivers are gone in the device panel, if not remove them. now that they are completly removed. shutdown. reinsert the sound card. reinstall the latest drivers. this is the sure fire way, unless your harddrive is corrupt or you are using the wrong drivers it shoudl work. also check and make sure your sound card is not broken hardware wise (there shoudl be a diagnostic prog with the card). you may just need to uninstall drivers, reboot, reinstall latest drivers. cause recognizing the hardware everytime you boot means the drivers you installed are the wrong ones. when did it stop working (ie after you install somethign?) it could have screwed somethign up.

did you do a hardware diagnostic and have it come back nominal?