heres some steps to trouble shoot the problem...
1) make sure that you did not install service pack 2 after you installed the drivers for the soundcard (if you manually installed it)
2) if you have another computer with the right slot open, plug it into that one and check to see if there is a problem with that slot.
3) make sure that its not your sound drivers, try un installing the drivers then re installing them
4) make sure that its not your speakers.
5) check the tech support website for the soundcard..
http://www.soundblaster.com there is always helpful info on them, and chances are that somone else has had this problem before...
6) if all else fails...e-mail sound blaster , and they will do anything in their power to help you out.