What is your configuration? You may try the gNewSense LiveCD...or the Ubuntu LiveCD...or the GParted LiveCD...to view the partitions. From there, identify, either by mounting them or looking on the screen, the boot, root, whatever. Finally, making note of this, use the original CD to install GRUB.
FOLLOW DIRECTIONS TO ACCESS THE ENCRYPTED DEVICES
AS GPARTED CANNOT. Be sure the system can use the crypto stuff. Then, install GRUB.
IF YOU EDITED THE FILE AT ALL OR ACCESSED IT...
Look for something like:
ls -a /whatever # /whatever is wherever I wanted to plop it
menu.lst menu.lst~ # the ~ is a backup
The backup might be there. Hope this helps