Help for error 1004
Quit the App Store of it's open.
Open the Finder. From the Finder menu bar click Go > Go to Folder
Type or copy/paste: ~/Library/Cookies
Click Go then move the com.apple.appstore.cookies file from the Cookies folder to the Trash.
Type or copy/paste: ~/Library/Preferences
Click Go then move the com.apple.appstore.plist file from the Preferences folder to the Trash.
Try the App Store.