When you say, "…all my icons are blank" I assume you mean the icons you see on your desktop and in Finder? It is unlikely that a properly executed "drag and drop" installation of any app would be the proximate cause of losing the system icons. Try dragging ~/Library/Preferences/com.apple.finder.plist to the desktop and then reboot. If that solves the problem then drag com.apple.finder.plist from your desktop to the trash and then empty the trash. You will, of course, have to reset all of your Finder preferences.
If that does not solve the problem, you can restore the finder property list to the preferences folder and replace the new copy that was automatically created when you rebooted.
joemikeb • moderator