1. In this case go to telinit 3 mode by pressing Ctrl+Alt+F2 and login as root
2. cd /etc/X11
3. rm xorg.conf
4. yum update kernel kernel-devel
5. sh NVIDIA* -k $(uname -r)
6. shutdown -r now
and it should start normally again...
A lot of time is spent on solving problems regarding software conflicts.
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Here you can find useful advice on how to solve problems quickly and ... forever!