Check the .xsession-errors in you home directory and the /var/log/ log files.
well , there was no .xsession-errors , so i can assum that there is nothing wrong with X , but i found another file called Xorg.log.1 . i checked this file also but there was nothing wronge.
i thought to reset GNOME to the original status. i downloaded some GNOME thems from GNOME website previosly. and i used them for a while but it efected the performance a lot. when i reset the thems manager to the default , i stoped having this delay. i guess i will never use GNOME thems again unless they are safe.