Cant view/read post – have_posts() never return true?

Hi all,
I am kinda frustrated with setting up WP now.
It already happened to me yesterday. And I resolved by removing everything and start all over from scratch. I can’t do this everytime I have this error….

After some tweaking on themes (mostly on layout, etc.), installing some plugins, I can’t view the post anymore.
Any thing that I have messed up??
Please advice me what to do.

<?php if (have_posts()) : ?>

		<?php while (have_posts()) : the_post(); ?>

        <div class="post" id="post-<?php the_ID(); ?>">
		  <div class="date"><span><?php the_time('M') ?></span> <?php the_time('d') ?></div>
		  <div class="title">
          <h2><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>"><?php the_title(); ?></a></h2>
          <div class="postdata"><span class="category"><?php the_category(', ') ?></span>  <span class="comments"><?php comments_popup_link('No Comments »', '1 Comment »', '% Comments »'); ?></span></div>
		  </div>
          <div class="entry">
			<?php if(is_category() || is_archive()) {
			   //the_title();
			} else {
			  the_content('Continue Reading &raquo;');
			} ?>

            <p class="submeta">written by <strong><?php the_author(); ?></strong>
			<?php
				if(function_exists("the_tags"))
					the_tags('\\\\ tags: ', ', ', '<br />');
			?>
            </p>

          </div><!--/entry -->

        </div><!--/post -->

		<?php endwhile; ?>

        <div class="page-nav"> <span class="previous-entries"><?php next_posts_link('Previous Entries') ?></span> <span class="next-entries"><?php previous_posts_link('Next Entries') ?></span></div><!-- /page nav -->

	<?php else : ?>

		<h2>Not Found</h2>
		<p>Sorry, but you are looking for something that isn't here.</p>

	<?php endif; ?>

This is the code on Index.php. I bet it’s not related to theme, as I have tried to set other theme and it doesn’t show any posts either.

Thanks in advance.

holmes