When the machine first froze, did you just switch it off, because you did not know how to regain control? If so, you have probably corrupted the file system and that has apparently prevented grub finding its files.
The first thing to try is to boot from the livecd, open a terminal, type
su to become root, enter the root password (
root for a standard livecd) when prompted, and then run
fsck -fy /dev/sdax where
ax is the letter and number of your pclos partitions. To find out which they are you can use
fdisk -l (that's a lower-case 'L'). You don't need to (and can't, in fact)
fsck the swap, but the
/home or whatever you have need to be done. They must be unmounted, but should be by default with the livecd. If not, use
umount /dev/sdax to unmount them.