9.1 problem

I have two computers using a 4-way kvm switch to share a monitor and a usb keyboard and mouse. One machine was upgraded to 9.1 the other is still 9.0. The problem is that if I set the switch to an empty channel (no signal to the monitor then) for longer than about eight hours overnight) and then go back to the channel the 9.1 is on I get no keyboard or mouse response. Sometimes I hear the two system beeps when the usb is initiated sometimes not. I plugged in another usb keyboard directly into the 9.1 machine-no response. So far the only way around this is to hit the reset button. Any ideas on what is happening here? Thanks, Jerome