cookies

I have a wordpress blog that I write to daily. I have a client that is running for mayor of our city and wants me to work a blog for him. He has set that blog up, sent me all of the information to login but WP has placed a cookie on my computer and now every time I go to log into His new blog I get sent to MY login and dashboard. Even if I write his address into my browsers address bar I’m automatically taken to MY page and there seems no way around this. I want to setup a different theme, permissions and widgets, but no matter what I do I’m taken to my dashboard. How do I bypass this so I can work on His blog?

Any help would be greatly appreciated guys.