Can somebody help me with my (X)HTML?

the problem is you are using tables. Tables make everything implode.

But to answer your question, seems to be some issue with your colspans.

honeslty though i would remake this with divs, so much cleaner, organized and easier to work with.

In your second row, you have a lone
<td>
that has no content and no close tag. I’m willing to bet that’s the issue.

But I agree with @wenn – this is revolting HTML. I’m guessing it was generated for you by some program. Ditch that program and rewrite it yourself as <div>s.

The they mean by <div>s is CSS. Look into redesigning that form using css

Actually, you’ll want to use <form> and it’s elements, perhaps a <fieldset> and <legend> or even a <h1> somewhere. <div>‘s really are overused as you can just style those elements without wrapping them in another <div>.