GX280 Peripherals Stop Working

I have six GX280's all of which have had this issue.  The motherboards have all been replaced but I still have the issue on some of them.  The keyboard, or barcode scanner, or mouse stops working.  Unplugging the device and plugging it back in works.  I also seem to be missing print jobs going to the parralel port on occation. 

I see this is a common problem with older models (GX240 ...). 

 

Please advise.  I can't keep having problems with these production line computers.

 

Running WXP SP2 with latest updates.