(1) Are you using the secure https:// login? If not then try using it.
(2) Exactly which browser and version of it are you using? If you aren’t sure click here to find out > http://whatsmyuseragent.com/
Note: If you are using an IE9 browser in compatibility mode that makes it render as IE7 and IE7 is not supported. To disable see > http://www.sevenforums.com/tutorials/1196-internet-explorer-compatibility-view-turn-off.html
(3) Have you done any troubleshooting?
a. Clearing your browser cache and cookies > http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=32050
b. Using the browser with all extensions or add-ons disabled
c. Updating the browser to the latest stable version (not a buggy BETA browser version) http://browsehappy.com/
d. Confirming third party cookies is enabled on the browser http://support.google.com/accounts/bin/answer.py?hl=en&answer=61416
f. Confirming Flash is updated http://www.adobe.com/software/flash/about/ and if required installing the latest version of Flash http://www.adobe.com/products/flashplayer/
g. Resetting your router and modem and rebooting your computer
then logging in using the secure https:// log-in
h. Trying another browser