WordPress plugins/login/logout/comment approval not redirecting.

My wordpress site have some issue. When user register on my wordpress site. and then a blank page display. User not able to return back to homepage. Once user signup on my site and then after that user also not able to login in my wordpress site. when user submit username and password then wordpress just display an blank page. e.g

when user Login user stay on same page.
http;//www.domain.com/wp-login.php but blank. it display nothing.

and also when i try to activate any plugin or deactivate. then again blank page display. But when i come back to previous page and then plugin page work fine. Problem is only in plugin section. it don’t display message that your plugin is activate/deactivate now.

i login with my admin account but not able to logout. when i do that again blank page show.

I enable comment approval features. but i am no more to approve my pending user comment. once i click approve and then again blank page display. and nothing happen.