Which browser are you using, and which version? (It's possible that a recent update to your browser means that the Ancestry website is no longer compatible with it or that an update to the Ancestry site means that it's no longer compatible with older browsers).
Check that you're using the latest (stable) edition of your browser. Then try a different browser. Most of the 'regulars ' around here, in AB's Technology section, would probably recommend Firefox as your first choice:
http://www.mozilla.org/en-US/firefox/all/
with Chrome as a close second:
http://www.google.com/intl/en_uk/chrome/browser/
(I love Firefox but I can't seem to get on with Chrome).
Safari would probably take 3rd place:
http://support.apple.com/kb/dl1531
with Internet Explorer definitely being a 'non-runner'!
Chris