Can't Update Software from the App Store

Question

The app store will not download any sort of update (iTunes or System Update). I click "install" and I have to "Agree" twice. Then I select "Download & Restart". The progress bar pops up and says "installing" then goes away. Under "Updates Installed in the Last 30 Days" it says has the "iTunes 12.1.2 update" and "OS X Yosemite Recovery Update" even though it never even downloaded and is still listed in the "Update Available" section along with "OS X Update 10.10.3 – Restart Required".
Please help. Thanks!

Answer 1

Back up all data before proceeding.
Triple-click anywhere in the line below on this page to select it:
/var/folders/zz
Right-click or control-click the highlighted line and select
          Services ▹ Reveal in Finder (or just Reveal)
from the contextual menu.* A folder should open with an item selected. Move the selected item to the Trash. You may be prompted for your administrator login password. Restart the computer and empty the Trash.
*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination  command-C. In the Finder, select
          Go ▹ Go to Folder...
from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.