Yesterday I was trying to install Ganglia in my virtual machine. After I defined Ganglia as a service I reboot the machine, but after that CentOS won't present the log in menu anymore.
I think it's because Ganglia service is blocking the system from starting properly, because I was able to show the start commands that the OS presents as shown below.
How do I fix that ?
Boot into single user mode and disable the service in other runlevels, then switch to RL3 (or 5) or reboot normally.
From the look of it, Ganglia is started in the foreground and does not allow the boot process to continue. Boot single as SvenW suggested or (if the VM makes it difficult) you can enter interactive boot by pressing 'I' in the first stages of the boot process.