is it not letting you go to main page of google? is it prompting you to put the security letters to know you are not a robot?
it happened to me last week. what i did is , i haven't tried to go to google for 1 whole day.. then i tried to google using incognito window, but error still shows up. i tried it again using the normal window. then it worked.. this time, incognito window is the one not working on google.