...on your main desktop view, verify that your finder preferences are allowing hard disks to show, this is under finder > preferences, on the top menu of your desktop...
...the short cut is by pressing apple and the comma key (,)...
...under "general" section you ought to have all those options turned on, also check the "sidebar" section, again, all options here are worth having on...
...if these are on and it still isn't showing then you have a more serious problem with hard disk mounting, which will require specialist software to fix...
andrew