Sorry, I have a complicated problem.

I have installed google adsense sidebox and fill in my adsense codes into the corresponding page in the "define page editor". However, when I click into google, no statistics was shown. Do I need to go through the google verification process?

I tried to use the "upload html" method for verification but it was failed due to something like:
"404 page returned 200 (successful code).....". Anyone know what it is?

Then I tried to use another method "code verification". It ask me to insert a code with "meta name" into the first page of my site inside <head> and before <body>. But then when I open index.html in my website root directory, there is no such code. Instead, there is some comments that the <head> code is load from "YourTemplate/common/html_header.php". Is this the file I should amend? Also, in this file, there is already a "meta name" tag already, should I replace it or keep two meta name concurrently?

Sorry for such a long question. Can any expert help?