Pretty simple really.
Just use the command
find / -name stage1
to find out which directory has Grub's system files stage1 and stage2. Then copy these two files into the directory /boot/grub.
Fire up a Grub shell at terminal, say the partition contains /boot/grub is the 2nd partition of your 1st hard disk known to Grub as (hd0,1) then Grub will be setup in the MBR by terminal commands
In the above the red
commands are inside the Grub shell while the others are Linux terminal commands.
The above, after a reboot, boots you to a Grub prompt with which you can boot any system manually. To boot the system automatically you need to write a menu.lst or Grub's configuration file.
We can suggest a menu.lst if you provide
(1) output of "fdisk -l" in a Bash terminal
(2) List of files inside /boot
Having said that there is no installed PC system that cannot be booted in a Grub prompt so it pays to know how to use it.