If you are blocking cookies, popups or ads or have any software that might
do so, they can block access to some sites.  Sometimes an incorrectly
configured firewall can block access.  If you've been doing anything with
the host's file or have software that makes changes in the host's file that
can cause such problems.

Sometimes you only need to clear out the cache.  Open Control Panel, open
Internet Options, on the General tab, click Delete Cookies, Delete Files
(accept the option to delete all offline content) and click clear History.
Note, after making any changes in the above, for example making settings
change in some security software, be sure to again clear the cache as a page
hung in the cache, even though it was the result of a setting may still
block access.