login page has redirect loop

I tried to login to the admin panel on my webpage yesterday, but after I wrote username and password i just got a page that says This webpage has a redirect loop. Also, when I tried to go back and login again ( in case I wrote the wrong password) the login page looks pretty simple. No wordpress lgoo, just plaine text. I haven’t done any changes on the webpage the last weeks, and I’ve contacted my server host, but they predictet that it was WordPress that have made some changes that made this happend.. Any idea where I should begin?

Thanx