Mouse has disappeared from multiple machines

I have several machines, multiple O/S’s where the ps2 mouse quits working. We have had 5 of them go out in the past week. This is not normal. Does anyone know of any type of virus that could be causing this? We use Symantic and they systems are comming up clean. We also tried anti-spyware.. No luck. We can plug in usb mice and they work fine. Thanks.