Why has my siteurl changed?

I am having huge problems. I’ve spent the last few hours trying to troubleshoot my way through this. I hope someone can help me.

My siteurl has been changed. we’ll call the original siteurl “http://www.mysite.com/wp” and it was changed to “http://www.mysite.com/wp/book”. Now my entire site is messed up and the admin pages as well. If I log in like normal, the admin pages don’t even show up…because they point to the folder “/wp/book” instead of “/wp”.

I have to manually type the URL of whatever admin page I want to see, but when i try to change the siterul, i get a message that says “Sorry, you need to enable sending referrers for this feature to work.”

I’ve tried installing the phpMyAdmin plugin, but it does not show up under “Manage” and when I try to activate it under “Plugins” it gives me the same error about enabling sending referrers.

All I need to do is correct the siteurl and everything will be right again in the world…How do I do that????

[moderated title to reflect question MH]