I installed Ubuntu 12.10 through DVD. Previously i had Win 7 with 500 GB internal HDD. It had 4 partitions. When installing Ubuntu, i had given the option of replace win 7 with Ubuntu. The installation has been complete. But the problem is, the computer section in Ubuntu shows 500 GB hard disk in the list. But, when i try to open the hard disk it shows error message as unable to mount. Please help.