first things first does your hard disk show up in the Computer folder in the Finder? you can get to Computer by selecting it from Finder's Go menu or pressing "command-shift-C". then check Finder's preferences. have you unticked "Hard Disks" under Show these items on the Desktop or Show these items in the Sidebar?
if you still cant see it copy and paste this command into the Terminal to show hidden files.
Code:
defaults write com.apple.finder AppleShowAllFiles TRUE
does your hard disk show up now? replace "TRUE" with "FALSE" in the above command to hide hidden files.