Use GRUB2 to Boot Linux(from grub manual)

1. Set GRUB's root device to the same drive as GNU/Linux's. The command search --file --set /vmlinuz or similar may help you .
2. Load the kernel using the command linux :

             grub> linux /vmlinuz root=/dev/sda1
   

   If you need to specify some kernel parameters, just append them to the command. For example, to set acpi to ‘off’, do this:

             grub> linux /vmlinuz root=/dev/sda1 acpi=off
   

   See the documentation in the Linux source tree for complete information on the available options.

   With linux GRUB uses 32-bit protocol. Some BIOS services like APM or EDD aren't available with this protocol. In this case you need to use linux16

             grub> linux16 /vmlinuz root=/dev/sda1 acpi=off
   

   Note: 
   linux /vmlinuz root=/dev/sda1 , the root stand for the "/" partition's position. When use command:set root=(hdx,y), this root stand for the "/boot" partition. This we must remember ! It's very important.

3. If you use an initrd, execute the command initrd  after linux:

             grub> initrd /initrd
   

   If you used linux16 you need to use initrd16:

             grub> initrd16 /initrd
   

4. Finally, run the command boot .