You could be experiencing a connectivity issue or a browser related issue. Would like to try these troubleshooting tips and provide some details about your environment that may help Staff help you resolve the issue?
clearing your browser cache and cookies > http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=32050
using the browser with all extensions or add-ons disabled
updating the browser to the latest stable version (not a buggy BETA browser version) http://browsehappy.com/
confirming third party cookies is enabled http://support.google.com/accounts/bin/answer.py?hl=en&answer=61416
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/
resetting your router and modem and rebooting your computer
then logging in using the secure https:// log-in see http://en.support.wordpress.com/https/
trying another browser
If those do not work for you then we need to know
(1) how you are connecting to the internet and to WordPress.com. The way you connect to the internet (mobile, satellite, DSL, dial-up) and to your blog, and how many proxy server jumps etc. it takes to connect can cause problems. There maybe be problems with your ISP and/or with the proxy servers.
(2) exactly which browser and version of it are you using. If you don’t know click here to find out > http://whatsmyuseragent.com/