this problem shows because boot.cfg file are loss ore damage. to repair this error you can follow this step :
1. grub rescue>ls
you must show your partition number, for example (hd0,6)
2. grub rescue>set prefix=(hd0,6)/boot/grub
3. grub rescue>set root=(hd0,6)
4. grub rescue>set
to check your step, must be look same of above.
5. grub rescue>ls /boot
show your boot folder on root partition
6. grub rescue>insmod /boot/grub/linux.mod
7. grub rescue>linux /vmlinuz root=/dev/sda6 ro
8. grub rescue>initrd /initrd.img
9. grub rescue>boot
oke you can boot into your linux, but this step are not permanent. to make this permanent follow this step :
$ sudo update-grub
$ sudo grub-install /dev/sda
$ sudo update-grub
oke you can try now,....
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