locked out of site, template missing, site still operates

i was trying to program the custom header to click through to my company site instead of just clicking back the blog home page.

I believe I was in the settings for either general or domains and i put my company website in as the link, instead of leaving it as the blog link.

next thing i know, the header is missing from my blog site and i cannot log in to my blog anymore. i clearly redirected something and i have no idea how to undo this.

insight/advice is greatly appreciated.