hey guys im new to joomla and i don't know what caused this problem, i had created a new template myself, and successfully installed it and it displays correctly, but when i try to edit the template in the backend it doesn't show any any html code it only shows a blank page in the editor... please help :(

There is probably a JavaScript error with the editor. Make sure your browser is up to date. You can also disable the editor with the global configuration.

The other option is to edit the template via FTP. The files are under /{joomla_root}/templates/template_name/