what do you mean you cannot get into it...
WordPress supplies two themes in its distribution for your initial use. You can switch between these two themes using the admin panel. Themes that you add to that directory will appear in the Administration Panels > Design > Themes as additional selections.
There are many themes available for download that will work with your WordPress installation.
To add a new theme to your WordPress installation, follow these basic steps:
If your host offers the cPanel control panel, and the theme files are in a .zip or .gz archive follow these instructions. Note: This assumes the theme you download is a compressed (zip) file and the files in the zip file are in their 'named' folder.
Note: You can also install and activate the plugin Get_Theme, to download themes directly to your blog.
To select the active theme for your site:
Your selection should immediately become active.