If I understand you correctly when you click on the button you want the iframe src to be changed. But when you click the target iframe main button the iframe becomes blank but if you check the console it gives you "Refused to display 'https://www.google.co.in/?gfe_rd=cr&ei=H1wbWOmhAavT8geWn6eYDg' in a frame because it set 'X-Frame-Options' to 'SAMEORIGIN'."
console error
Which, if i undestand correctly, is caused as the target url is on a different domain i.e google.com. I would suggest upload another page on the same domain & check.
But if you still want to display a webpage from a different domain then How to set 'X-Frame-Options' on iframe? may help.
Incase it is something else then a little more elaboration is required.