Dear friends,

I have some problem in my image attachment page, when i open single post it's as it is, but when i click on image it opens attachment page but template changes. means sidebar goes off (it's by default i know, but i don't want to remove sidebars). and background also goes

can any one knows how to solve this problem.

snapshot link of both single and attachment post is given below.
single post : Image
attachment :Image

If you theme has an attachment.php then it is using this file to display the image, which in that case you would need to edit this file to your liking. If you don't have an attachment.php then the theme is most likely using index.php which is the default. You can always add attachment.php to the theme if it doesn't exist and then your attachments will open in this file.

Here is a link to information that explains the hierarchy of Wordpress themes