If it shuts down abruptly when a device is plugged in, the most likely cause is a short circuit somewhere. Maybe a recent power surge damaged the USB controllers in all the computers at once. Boot to a command prompt or some other non-Windows operating system, to determine if it is really a hardware problem. When you mentioned that it needed to be unplugged and replugged for it to power up again, that is a certain symptom of the PSU shutting off because of a short circuit. If the shutdown is accompanied shortly after by a sharp squealing or whining from the PSU, it's definitely a short circuit.