What is W3C Validator ?

And how do I get rid of it?
I have a page http://familytrees.genopro.com/nancyhandke/handke/
where when it arrives, a yellow warning is displayed for 2 seconds then
disappears. It is too fast to read.
Your logo appears as a button linking to your site. 
The page is also 'all messed up.'
I did not ask for this service to interfere and I don't want it.
Please, please can you tell me how this service is getting mixed up with
this URL 
and how do I remove it.
 
In appreciation
Stu Mason