I just got a Raspberry Pi model A in the post. This is my first model A, (I have 2 model B's). The issue I have is that if a USB device is plugged into the pi. (Tried a Wireless keyboard dongle, WIFI dongle and a powered hub) The pi refuses to boot. The power lights just do not come on. When I plug out the USB device, it boots. However as I can not plug in a keyboard or WIFI and ssh in I can't do much in the way of diagnostics. Any suggestions why this might happen? All devices, power cables and hubs work with the model B's.