Fixing ARM JTAGS
From Null Space Labs
Open up the JTAG Download SAM-BA From Here and install.
Short Location A, power up, wait 20 seconds, power down
Short Location B, power up, wait 10 seconds, power down
Reconnect USB, comm port should appear
Flash, say yes to unlock, say no to relock
Led should start flashing
Sometimes SAM-BA takes 60 seconds or so to load.