Please work through these steps below and then report your specifics back to us.
If you are not running one of the browsers and versions listed at http://browsehappy.com/ please try upgrading or switching first.
If you are running one of the browsers and versions listed at http://browsehappy.com/
(a) Try clearing your browser’s cache http://www.google.com/support/accounts/bin/answer.py?hl=en&answer=32050
If applicable see here for instructions on how to clear the cache for Chrome and Safari on the iPad:
(c) Disable all browser extensions or add-ons temporarily.
(d) Try enabling HTTPS: http://en.support.wordpress.com/https/
Add both *.wordpress.com and *.wp.com to your list of trusted sites under the Security tab. Make sure to uncheck the box for “Require server verification (https:) for all sites in this zone.” http://en.support.wordpress.com/https/#frequently-asked-questions
6. If you are not successful let us know:
(a) How you are connecting to the internet and to WordPress.com.
(b) Exactly which browser (and version of it) you’re using by checking here if necessary http://www.whatbrowser.org/
(c) And what any error reports you receive state.