I have a failing hard disk and need the command prompt to list the partitions and to run the Linux equivalent of scandisk and mark any bad sectors. Also the command to go from safe mode to normal desktop.
You need to run either FSCK or badblocks (personally I would run FSCK) a full list of commands for both can be found here:
http://linux.die.net/man/8/e2fsck
http://linux.die.net/man/8/badblocks
Switching from the CLI back to the GUI should be Ctrl+Alt+F7