Strange one... Have the PCI-express X-Fi card, been working fine until today. Can get sound from the headphone jack, but not the normal speaker outputs. Speakers work connected to anything else, but no longer the normal speaker outputs from the sound card. I've tried updating drivers but no luck.
+1^ seems a very logical explanation with that sound card you should be able to set another sound output port as your default stereo output port try change it to a different physical port on the sounds card and see if that makes any difference.
Uninstall the SoundBlaster in the Device Manager (DO NOT uninstall the Drivers) and then restart the PC and when Windows starts it should detect and reinstall the sound card. This may fix it.
If not, reinstall the Creative drivers (get the latest drivers from the Creative site). You should have the What You Hear (what SoundBlaster calls the "System Mixer") and the other missing recording devices.