When my workstation was doing this it was due to an external drive that was having issues. I had a mirror set with an external eSata and the controller on the eSata kept losing connection to the drive so every time the mirror would try to sync the USB would stop working too since it couldn't find the drive. ZFS is incredible because it never lost anything however I digress. While I know your issue may not be the same as mine was. Another thought is if you have a USB mouse you may want to switch to an older PS/2 mouse. The PS/2 port has an interrupt assigned to it while USB does not have that type of priority to the CPU. Either way it sounds like a hardware issue more than a software one. I hope this helps some.