Speakers failed: right sorround and left

I have a 5.1 speaker system (Hercules-Guillemot XPS 510) connected to a nForce2 OnBoard sound. I never had problems until now, but now these two speakers failed. I already checked all the cables. I also have 5.1 sound activated in my nForce control program. Does anyone ha´ve a idea, what could be the reason for this failure?

AMD Athlon XP 2700+
Epox 8rda+
Thermaltake Volcano 7+
2x256 MB PC2700
Creative GeForce 4 Ti 4800 (4600 Chip)
Chieftech Case
WD 80GB/8MB HDD
16x48 DVD-ROM
20x10x32 Burner

It is set to 5.1, and 5.1 also workes, when it is set to something else. The nForce2 control panel controls this, not the Windows control panel.

I connected the speakers to the line out of my protable cd-player, and these two speakers still dont work. I think, that the problem is rather the subwoofer than the speakers itself, because its unlikely that 2 speakers fail at the same time, because the speakers arent directly connected to the pc/line out. The speakers are connected to the subwoofer and the subwoofer is conected to the pc.

Also, I recognized, that the subwoofer always made sounds at the same volume, if I was connnected the cable for central and subwoofer or another one.

So tomorrow I will go to my shop and RMA the speakers (I only have them three months now).

AMD Athlon XP 2700+
Epox 8rda+
Thermaltake Volcano 7+
2x256 MB PC2700
Creative GeForce 4 Ti 4800 (4600 Chip)
Chieftech Case
WD 80GB/8MB HDD
16x48 DVD-ROM
20x10x32 Burner

This is not the problem: everything is set to 5.1, tge subwoofer is woofing and as I posted before, that two speaker aslo dont work when I connect them to the line-out of my discman. <b>So it definitly is a problem w/ the subwoofer or the speakers.</b>

AMD Athlon XP 2700+
Epox 8rda+
Thermaltake Volcano 7+
2x256 MB PC2700
Creative GeForce 4 Ti 4800 (4600 Chip)
Chieftech Case
WD 80GB/8MB HDD
16x48 DVD-ROM
20x10x32 Burner

I have now found out, that when I turn the volume of the speakers louder, the problem is gone, even when I turn it lower in Windows afterwards, so that the resulting volume is the same. Because of this I will not RMA it, althought I still could, but why should I make that work, if it also can be solved otherwise? I also asked the guy in the shop, if the problems I have now could lead to bigger problems later, but he said, that he doesnt think so.

AMD Athlon XP 2700+
Epox 8rda+
Thermaltake Volcano 7+
2x256 MB PC2700
Creative GeForce 4 Ti 4800 (4600 Chip)
Chieftech Case
WD 80GB/8MB HDD
16x48 DVD-ROM
20x10x32 Burner