Well, there is the possibility that it is just dead and there is no fix. You could disable it in bios and buy a new sound card.
If you want to try to fix still these are my suggestions:
check bios make sure that the device is active(sounds like it is), look for a setting that says "plug and play OS" and set to yes. Check your IRQ settings, disable anything you dont use(serial port, IR port, etc..). You can try to altenate manual setting and auto setting the IRQ on the soundcard.
Make sure both your motherboard firmware and the drivers you are trying to install are up to date. disable antivirus during install.
If you have intel inegrated gfx, they have been known to cause strange problems with other drivers. I think updates are available.
good luck.
PS - what does "slow" sound sound like?
