After upgrading Magento unable to log into admin

If you just did an upgrade to magento or for some reason you try to log into the admin and you cant...and you do not get any errors...its more than likely a caching issue.

remove everything from the var/cache folder

Get to your root of your magento install

cd /var/www/magento_root_location_on_your_server/

rm -rf var/cache/*

Dump your browser cache/history and try again..OR just try a different browser, I bet it will work.