Best way to fix grub problem

Try the following

grub rescue > ls

grub rescue > ls (hd0,msdos2) # let's assume this is the linux partition 

grub rescue > set root=(hd0,msdos2) 

grub rescue > set prefix=(hd0,msdos2)/boot/grub # or wherever grub is installed 

grub rescue > insmod normal # if this produced an error, reset root and prefix to something else .. 

grub rescue > normal

Run the following after you successfully boot

sudo update-grub 

sudo grub-install /dev/sdX 
# where /dev/sdX is your boot drive.

If you have to copy a whole linux system, you could use Clonezilla