-Reboot, test
-Reinstall drivers, test
-Make sure you are using the right driver and there are no odd issues listed in device managers. (Ex. disabled/conflict/other issue)
If it’s not being detected at all
Built-in:
-Make sure it is turned on in the BIOS
-Make sure PnP OS is turned on, again in the BIOS as it might prevent windows from picking it up if it’s off on odd instances.
Add-on:
-Shut down the computer, reseat the soundcard.
-Upon reboot if it’s not picked up try the card in another system
If it’s not detected then it’s probably dead, or there is another issue I missed. But this covers most of it.