Hello I have found the solution:
add these lines to xorg.conf:
Option "AllowEmptyInput" "off"
But I don't know why these happens beacause I have never add these to my old xorg.conf and it do works well until my last upgrade.
But now only root can log to kde , My mormal user account could not login.
the error message is as follows:
call to lnusertemp failed(temporary directiries full?).
and when return text mode ,more message is like this:
(EE) config/hal : couldn't initialise context: unknown error (null)
xset: bad font path element (#23), possible causes are:
Directory does not exist or has wrong permissions
directory missing fonts.dir
incorrect font server address or synatax.
Error: "/var/tmp/kde-cache-hudi" is not a directory.
startxkde: call to lnusertemp failed(temporary directiries full?).check your installations.