i had this set two years ago. I recently experience the problem:

Sometimes, it just works fine for all 5 pieces, sound is nice.

but most of the time (recently i experience more and more), esp after i restarted the computer, the subwoofer works but the rest 4 have no sound, and experiencing some "hissing" sound.

I switch the control to headset, no problem. My sound card is creative extrememusic. I used creative diagnostic tools to do the speaker test. "front left, front front center, front right, rear right......" are not from these dedicated speakers but subwoofer. In this case, it just likes the situation i described above,(the subwoofer works but the rest 4 have no sound, and experiencing some "hissing" sound. ) However, it "could" possibly work after i switch the control panel between headset and speaker manytimes, depends on luck!! thus, sometimes, the Creative test can go through, every speaker just works fine. This really confused me. It works like I am flipping the coin. Anyone has the same issue or idea what's going on? Thanks in advance

BTW,  i recently experienced one power outrage, is it the possiblity of causing the problem? if so, any advise for some replacement unit