I have had 5 pairs of Shure's and love all of them, but i listen to a lot of music: 3 hours a day. The Shure's are great but they do short...My suggestion would be to put your iPod flat out on a desk like your notebook would be so that the Shure's wire are at the exact same angle and what not, chances are that it's the Shure's- headphones will short depending on the way the wire is usually.
Shure's are covered by a two year warranty and you can get them replaced by Shure if you bought them from a legit seller/authorized dealer like the Apple Store, chances are if you bought them from eBay, you probably are out of luck.