Well let me explain.
There must be something that is overriding the original file checkout.tpl, it's the only thing that can make it.
Normally in checkout page by default you see a clean page.
No header, no footer, only your cart and copyright thing, and that's what checkout files says to do but it is not doing what it should.
Some module must be overriding original file.
And @D. Tengler thanks for your good help