Asrock 970 extreme4 not finding keyboard

Just upgraded mboard in PC to an Asrock 970 extreme4 ... all seemed to be working fine for a few days until this morning and it turned on and froze at BIOS splash screen. DrDebug showed it was waiting for console input device. Tried a couple of different keyboards in both PS/2 and USB sockets an no change. After a short depressed pause I tried again shuffling keyboards and connections and suddenly it booted ok, tried a few other combinations and it all failed again. Eventually going through the permutations I discovered the problem. Last night I'd needed to write something onto a microSD card for my phone and when doing this found my card reader had come unplugged from its USB cable - and also the reader has a USB hub in it with my Logitech G25 wheel plugged into it. It appears that having that plugged into USB (possible fact its power input is not plugged in is relevant) causes the mboard to fail to find the keyboard!

So problem solved ... maybe someone else will have the same problem and find this info helpful!