i wonder if one of your coils is busted inside the mic
anyways i know the description of that mic says "vocal mic" but it is ment for an on stage mic for performers. not the ideal mic you would want to record vocals with in a studio, home, or any situation unless you were recording a live performance or you were an opera singer or stevie nicks and even she used a different sennheiser mic.
my suggestion would be to get rid of it, sell it, pawn it, whatever and use that money towards a condenser microphone. i've heard the usb condensers are good and ive heard that some suck. i have never used one, my microphone experience is mostly in more high end top brand mics. i dont know where you live but guitar center sells decent quality condenser mics for under 100 bucks. you can get the same mics on musiciansfriend.com .
i will say this till the day i die, never record vocals with a dynamic mic. escpecially if you rap. condenser mic is what you need.
if it is a cable like rukas is saying you can fix that yourself. i make my own mic cables and instrument cables. it is not hard you just need a soldering gun.