Your files are still there, you just need to chroot into your install. Something like this.

1) Boot from CD.
2) mkdir /mnt/gentoo (if it doesn't already exist)
3) mount /dev/hda3 /mnt/gentoo (hda3 being the root partition for your Gentoo install on your HD... yours may be different)
4) mount /dev/hda1 /mnt/gentoo/boot (hda1 being your boot partition for your Gentoo install on your HD, yours may be differentl)
5) mount -t proc none /mnt/gentoo/proc
6) mount -o bind /dev /mnt/gentoo/dev
7) chroot /mnt/gentoo /bin/bash (This will take you "into" your Gentoo install on your HD, as though you'd booted to it)
8) env-update (just in case)

If grub crashes again for some reason, you shouldn't have to reboot (and you really shouldn't ever do that, especially with something like grub that's editing your MBR ). Instead hit CTRL+C to kill it. Grub shouldn't be crashing though. Something's not good, if it does.