Hi Hadi Kamell,

Could you please give us some more information? like: Were you doing something in Admin Aera, or did it happen just when you wanted to login? Does the rest of the site work correctly? Wasn't you server offline when you wanted to go in Admin Aera?

After you have answered the questions and gave some more info, I will try to help you further. 

Great_Day

Hi
i was work at my host ( with oxwall files)
so i dont what of my jobs was wrong and this error occurred
by fire fox, after login, admin page becomes blank
thank you

Have you edited the .php files manual? If not than you could try to reinstall and use your existing database. Everything should be fine than. You should do this than: http://www.oxwall.org/forum/topic/3093?page=1#post-14564

But to be sure nothing will happen to your site and everything will go right, you should first test this on a localhost (Xampp, Wampp etc). There you can test it. If it works than, you can do it on your host. 

yes i should reinstall it :|

Reinstalling doesn't mean you will lose all of your data. If it is saved in the Database, you will lose nothing. (if you don't forget to backup the database ofcourse). But if you have edited the PHP than you may lose some things...

can i re-upload update pack (from 1.2.5 to 1.26) ?

I would recommend you to update automaticly. As it will be safer to do. 
Otherwise you should look at this:  http://docs.oxwall.org/install:update#manual-update

woww!

solved!
i was re-upload the update pack and true and then false devemode!

thank you Great_Day

Have a Great Day , greater than yesterday