Empty value of a search form

Empty value of a search form

I want to search in a adress book from a page which I am developing. The
adress book is a content of another page and the url of the adress book on
this page is http://example.com/start.php. This adress book has its own
search field, which I will use for my page. I have written the following
search form:
<form action="http://example.com/start.php" method="post" target="_blank">
<div>
<input type="hidden" value="adress" name="cmd" />
<input id = "adressinput" name="search" type="text" title="Search in the
adress book [ctrl-f]" accesskey="f" value="adress book" />
<input id="refresh" title="refreshnow" name="refresh" type="image"
src="icons/Downloads/arrow-circle-single.png" class="iconbutton"/>
</div>
</form>
The problem is that, when I write somethung in the text box of my form and
after that click on the icon refreshnow, the page
http://example.com/start.php (the adress book) is displayed, but the
search field of the this page has still an empty value and I don't get any
result, of course.
This wasn't my first search form. I have written similar forms and they
work, so, I have no idea why it doesn't work.