It's been over 10 years since I bought these headphones and consider them one of the best purchases I ever made. Wear them 4-6 hours a day and just started having problems with the sound cutting out on one side last month. Sennheiser has a flat rate of $150 for repair of the HD580s which means I'm going to spend $25 more to repair them than I spent to buy them brand new but still worth it. I'm using some other cheap headphones that I picked up at Best Buy while I'm waiting for my 580s to be returned and am not enjoying the experience.
Check the cables right where they plug into the driver cups, that's what was wrong with mine. Just had to order some new HD650 cables from Sennheiser and that fixed it.