[ubuntu] UBUNTU live CD and Front USB ports

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http://ubuntuforums.org – I can run UBUNTU from a pendrive from a rear usb port, but not from the front usb ports. If I use a facility in UBUNTU I can see a pendrive at the rear and also one in front, if inserted. Niether will mount on clicking. I can't see the front pendrive in Libre Offce (wp), so I can't save or open files. I have not tried to see the rear pendrive (OS). How can I get the front usb ports to function correctly ( I have recently installed a re-conditioned Dell motherboard to repalce a faulty mobo - both same types) Thanks (Hardware)