This is a copy/paste message from other site that explains perfectly my problem.
Just bought a new K55 keyboard earlier this week and things were great for the first two days, today though has been a big headache. What's happening is, when going from a COLD Boot, my computer hangs before Bios. This is only happening when my K55 is plugged in to any, USB 3.0 or USB 2.0, port. The only solution that's actually done anything is unplug/plug the K55 back in or turn off/on again pressing On button. My computer boots perfectly fine with another keyboard plugged in so long as the K55 isn't plugged in.
However, when I restart instead of a full shutdown, my PC boots perfectly fine with the K55 plugged in.
Anyone with this issue?