try restarting your computer,
also. Cookie checks for the existence of Safari's Cookies.binaryCookies file.
to make sure you have the file, visit a couple of sites in Safari NOT in private browsing mode. also if you have any other system cleaners. they may be removing the cookie file. (onyx, ccleaner etc...)
If you disable any Cookie timers you may have enabled.
login to Google
expand the Google.com dominion Cookie
look for any red coloured cookies
highlight the NID cookie
control-click (right click) to show the contextual menu
select Add to Whitelist