CANT LOG IN OR SEE MY SITE! 'This webpage has a redirect loop'

HELP! whenever i go to try and log into the back end OR visit my site it comes up with an error page ‘This webpage has a redirect loop’

and the address changes to – /wp-login.php?redirect_to=/wp-login.php?redirect_to=/wp-login.php?redirect_to=/wp-login.php?redirect_to=/wp-login.php?redirect_to=/wp-login.php?redirect_to=/wp-login.php?redirect_to=/wp-login.php?redirect_to=/wp-login.php?redirect_to=/wp-login.php?redirect_to=/

What can i do to fix it?!

i did reccently install an ‘members only’ plug-in that redirects you to the log in page………..