Last night i decided to upgrade my NVIdia driver to the latest version (9746). The installation was done perfectly and i could start the graphical screen normally like i had before. The problem started when i wanted to log off my account and switch back to text mode (i used run level 3 as the default in my Slackware system). Instead of switching back to text mode, the screen was blurred (like in one of KDE's screen saver) and it was similar like an old VGA cards. There's nothing i could do (even the keyboard didn't respond at all), so i had to use the power button to shut down the system.
Next, i tried to reproduce the bug again and it happened again, so i made a conclusion that the latest NVIdia driver is broken (or have some glitches inside), so i decided to revert back to previous version which is perfectly working before i upgrade to the latest version. Luckily i haven't delete the packages, since i usually delete them after i managed to upgrade.