I'm wondering if the USB ports are being overloaded by having both mouse and flash drive hooked up at the same time. That's why the keyboard is unresponsive until you remove a device. Second, there may me a slight latency programmed in the keyboard's ROM. This could be throwing the timing off and preventing the computer from recognizing the keyboard. But that seems a bit far-fetched to be true.

To fix this problem, I would start by placing a POWERED USB Hub in between the keyboard and computer. See if the problem still occurs. If not, then the USB ports were underpowered. If they occur again, then the keyboard should be the problem. I would then replace the keyboard with a different one.

73s 8)