My K70 MK2 is doing the same and I am pretty close to giving it away for free. I have spent so much time trying to figure out what is wrong. Its def the keyboard.
Different USB
Latest Bios
Latest drivers
Different PC
Hold ESC for 5 seconds
BIOS Mode
All this and the POS doesnt work and I have to use a cheapy wireless Logitech to use my gaming rig to browse the internet and type this post.....