I can't seem to hear my music when played on my PC properly when using my headphones (it works when using speakers). Instead, I get the sound through one "ear piece" but not through the other. This problem is recent. It was okay, even with crap headphones, before.
I'm using Dell with Windows XP2 with Service Pack 2 installed and updated etc.
From past experience it is usually where the wire goes into the jack plug it gets damaged here dueto the wire moving back and forward or being wound too tight around a music device - as these wires are about as thick as the hair on your head they are very easily damaged.
Well i can't really say what is wrong other than that the wires may be damaged but as you say it does seem a bit odd that all 4 pairs of headphones have the same fault on different pieces of equipment.
I had this problem on my seperates system just before Xmas. The cause was due to dust in the socket itself. I turned off the system, very carefully placed a cotton bud in the socket, twisted it a few times, and a very black swab came back out. Its been working ever since.