I concur with pixellany's view and suggest the OP to try the terminal method as follow
1. Boot up Mepis Live CD but instead of choosing a system to boot press "Esc" immdiately. You will be warned that you are leaving the graphic screen. Select Ok and now you are in text mode of Grub. You then press the "c" key to talk to Grub directly. No middleman involved everything from the horse's mouth now.
2. You ask Grub to tell you which partition has its menu.lst by command
Grub should reply with something like "(hd0,0)"
3. You restore Grub by terminal command
Adjust the red
bit to suit your own circunstance.
4. You now boot up Mepis by commands
Report any error message if the above fails.