Weird USB problem - MPro OS 10.7.5

[macmesser]

MPro 2009 5,1 flashed from 4,1, OS 10.7.5. Mouse intermittently becomes unresponsive. Noticed this about a week ago and changing the Mac usb connector fixed at first. Still losing mouse and today lost keyboard too. Switching MAc usb port didn't help. Hard reboot don't help at first. Switched mouse and keyboard and problem reoccurred. I know second mouse and keyboard are good and also have been printing from the external usb connections, so they seem to be good too. Could this be a driver conflict? Mac is stock except for memory and drives. Only printer drivers installed: two cannon, one lexmark, one brother all-in-one (which has a manager utility startup item). The only other thing that might have some drivers is parallels 8. Today the problem occurred and I lost mouse and keyboard. Switching external usb ports did not help, even to known good ports from which I could print. I have been regularly running software update which could be the cause. Any insights appreciated.