(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. Also note that the main dashboard isn’t designed to work with touch devices through the tablet and smartphone browsers.
(2) Are you using the secure https:// login?
(3) Exactly which browser and version of it are you using. If you don’t know 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
Have you done any troubleshooting? These are the troubleshooting steps we take whenever any issues like this arise:
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/