Site is not opening

Try:
– switching to the default theme by renaming your current theme’s folder inside wp-content/themes and adding “-old” to the end of the folder name using FTP or whatever file management application your host provides.

– resetting the plugins folder by FTP or phpMyAdmin.

– re-uploading all files & folders – except the wp-content folder – from a fresh download of WordPress. Make sure that you delete the old copies of files & folder before uploading the new ones.

Is it possible to find problem if i copy and past all of my header.php code here with in this question box?

Did you try any of the suggestions posted above?

I am not clear about your instruction in above.

Which part?

Uploading all files and folders from word press.

I’m sorry but what part of that do you not understand?

Before uploading word-press again how to take back up all files through FTP?

Why would you need a backup of those files? Almost all of your site’s content is stored in your database – not in any files. As long as you avoid the wp-content folder, you will not over-write anything that relates to your site’s content or display.