Post publishing category select ( custom made page )

Hope somebody can help me solve this, I am struggling for more than 2 days. I have a custom post publishing page and I want to select categories for the post from categories dropdown, and use the value selected. I don’t know what im doing wrong but cant get it to work. It allways publishes the post with uncategorised. Here is the code.

// Category exists?
if (!empty($_POST['video_category'])) {
$video_category = $_POST['video_category'];
} else {
$video_category = 'Please select a category';
}

$my_post['post_category'] = array(prep($row['video_category'])); 

<select name="video_category" class="widefat mid">
 <option value="video_category">Select Category...</option>
 <?php
  $categories=  get_categories('');
  foreach ($categories as $videocategory) {
  	$video_category = '<option value="/category/archives/'.$videocategory->category_nicename.'">';
	$video_category .= $videocategory->cat_name;
	$video_category .= selected($videocategory, $_POST['video_category']);
	$video_category .= '</option>';
	print ucfirst($video_category);
  }
 ?>
</select>