Hello, I've got a Early 2009 Mac Pro 2.93 quad core, 4870, 16GB of OWC ram. I've been experiencing a weird problem where the USB will completely cut out after working for a while. When I'm using a USB mouse, any amount of time after startup, the mouse and the keyboard stop working. If i plug in another USB mouse, the light will come on, but it doesn't work to move the cursor. If i share the screen from the MBP, i can control the Mac Pro perfectly well. There doesn't seem to be any particular action that triggers the USB to stop functioning. I don't have anything but the keyboard and mouse wired by USB. I have a eSATA PCIe card, but that's it for added cards. I'll keep experimenting, but if this sounds familiar to anyone, help would be appreciated. Thanks. EDIT: I did reset the PRAM once, and also disconnected the power supply from the wall for a few minutes.