7
Sounds like your cache directory has the wrong chmod (permissions). Log into your site's ftp account and chmod the following directories to 777 (read/write/excecute):
/cache
/templates_c
/uploads
If that doesn't fix your problem, you may want to check your firewall logs (if you run a firewall) and see if it is blocking your domain. Likewise if you are using a cookie blocker. You may also want to make sure you can accept cookies from your domain in your Internet settings for your browser.
Good Luck!