How to recover a linux redhat 6.4 server while rebooting it got struck. How do I troubleshoot the issue as it's not showing grub also in Rescue mode?

Each time a Linux system boots, GRUB flashes by on the screen while it performs a brief countdown. The default countdown on many systems is five seconds but the actual countdown period can be adjusted. GRUB loads the Linux kernel and initial RAM disk image into system memory then fires the system up. When everything goes well and GRUB is finished with its task, the system successfully boots into Linux.

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