I've read about dead strings, among both guitarists and bassists. But in over 40 years of playing I'd never had one ... till today. I've used Slinkys for as long as I can remember on my guitars and basses and they've always been perfect. I put a set of xtra lite Cobalts on Tuesday and fell in love with the tone and the feel. I get home today and start playing my SR370 and the D string is dead as a door nail. It was perfect last nite. Today it sounds like the nut is bad or it's grounding out against the fret board. I raised it up 2 miles off the fretboard with no change. It's quiet and zero sustain. Replaced it with the D off the previous set and the old one is pefect. Any ideas? I assume this is what you call a dead string? Why did it die after 3 days? Weird.