First, reboot your PC & see if it helps.
If not, uninstall the card, drivers & software, then reinstall everything. Follow this method click here.
I know the above sounds silly but TRY it.
Every once in a while, for no good reason my Audigy 2 stops working - no sound. Uninstalling, then reinstalling the lot & a reboot works every time.
If no joy with above click here, & on "No sound from your Sound Blaster card" & follow the troubleshooting steps.
Where did you get the card from may I ask? Is it brand new? If you're unable to get it to work despite trying everything you may have a dead card??
Good luck, G