I turn my site off..
how do i edit tat particular page shown when its turned off ?
which file is tat?

i wan to add pictures of underconstruction and also some contact onto tat page..

Easy: it's a template. Go to system admin -> templates. If you only have the default template set, then you will have to clone it because you can't edit the default template set (because that set is the one you can always fall back on). Once you have cloned the default set, go to the SYstem templates, and edit the system_siteclosed.html template (NOT the file!). Then, in the system admin -> preferences -> general settings page, make the cloned template set the active one.

Herko