my first theme

Hi.

I’ve been designing themes, but modyfing existing themes. I erase all the style.css and most of the index.php of the themes… but I DON’T WANT TO KEEP ON DOING THAT… so i did this:
1- started a simple style.css, index.php, sidebar.php, header.php, footer.php
2- uploaded to the server
3- the “Theme screenshot” appears in control panel at Presentation-theme link. but…. it isn’t working. What steps am i losing? What may be the things that i do wrong?

4- Is there any URL where i can download a simple & clean theme where i can start my own or something like that? I checked all wordpress docs. But it still doesn’t helping me.

5- Sorry about my english. ??