previous/next_posts_link(); doesn’t work with new query

Why previous_posts_link(); and next_posts_link(); doesn’t work with the following code?

$args=array(
  'post_type' => 'post',
  'post_status' => 'publish',
  'posts_per_page' => 10,
  'caller_get_posts'=> 1
);
$my_query = null;
$my_query = new WP_Query($args);
if( $my_query->have_posts() ) {
  while ($my_query->have_posts()) : $my_query->the_post(); ?>

<?php the_title(); ?>
<?php the_content();?>
<?php endwhile; ?>

<?php if(function_exists('wp_pagenavi')){ wp_pagenavi(); } else { ?>
<?php previous_posts_link(); next_posts_link(); } ?>
<?php wp_reset_query(); ?>

Secondly I put the following code in page.php and it works but when I click “NEXT POSTS LINK” (which appears with this loop) I’m redirected to blank page with only one link that is pointing to the page I just entered.

$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
query_posts('cat='.$category.'' . $query_string . '&showposts=9&paged=' . $paged);
?>
<?php if (have_posts()) : while(have_posts()) : the_post(); ?>
<?php the_title(); ?>
<?php the_excerpt(); ?>
<?php previous_posts_link(); next_posts_link(); } ?>