[CentOS] big problem at boot

I restarted the a Centos 5.6 server tonight and I ran in this issue:

I was able to boot.
Then instead of a normal boot with graphical interface the system requested :
'Enter run level'
'INIT'
I typed 5
then I got 'INIT: no more process left in this run level

How can I recover from  the situation?
This is a production system back-up are made but left on the disk and transfer at the end of the day into an other system

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Michel Donais
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