You may have broken grub. Know how to fix grub error 15: file not found issue on CentOS & Ubuntu.

If you have updated your system and rebooted it without copying grub.conf to the boot directory, you may have broken grub.

To fix this you need to firstly mount the CentOS DVD (preferably the one that matches your operating system version). See: https://www.vpsblocks.com.au/support/Knowledgebase/Article/View/33/0/mount-a-dvd

You need to access your VPS via the web based console, see: https://www.vpsblocks.com.au/support/Knowledgebase/Article/View/28/0/how-can-i-get-console-access-to-my-vps

You can then send a ctrl-alt-delete and enter the DVD boot mode.

Choose to load Linux Rescue

When prompted to mount the operating system choose 'Next' or 'Yes' to do so. Or if prompted for a rescue image, just select hard drives then /sda1

This will mount your entire VPS at /mnt/sysimage

Type:

• cp /mnt/sysimage/etc/grub.conf /mnt/sysimage/boot/grub/grub.conf
• reboot

Now remove the CD through the DVD control panel. Your system should now boot.