Many Gmail users that use Internet Explorer 7 may have been experiencing issues when attempting to login to Gmail. Well good news, sort of. The problem is yet to be resolved by the Gmail team but their is a patch to the problem in the meantime. Use the following steps to access your Gmail account if you can't do so the typical (basic) way.
1. Use IE7 to access the newer version of Gmail at http://mail.google.com/mail?hist=0
2. Set your IE7 preferences to always clear your cache when you close IE.
3. Use IE7 to access the classic version of Gmail at http://mail.google.com/mail/?ui=1
4. Access your account with another browser such as Mozilla Firefox.
Hopefully this helps. If not you may have to wait until the Gmail team fixes the current issue with accessing Gmail via IE7.