Boot from your ArchLinux live cd again and in a command prompt as root run the exact following.
mkdir /mnt/root
mount /dev/sda3 /mnt/root
mount /dev/sda1 /mnt/root/boot
cp -a /dev/sd* /mnt/root/dev/
chroot /mnt/root
mount /proc
cat /proc/mounts > /etc/mtab
grub-install --recheck --no-floppy /dev/sda
umount /proc
exit
umount /mnt/root/boot
umount /mnt/root
reboot
Depending on what you did trying to setup autofs, you might want to check that /etc/fstab or /boot/grub/menu.lst files are valid while you are chrooted in your system (after mount /proc above).
There is also one more (shorter) way this can be done. Not sure if it is possible with the archlinux live cd, but probably is.
mkdir /mnt/root
mount /dev/sda3 /mnt/root
mount /dev/sda1 /mnt/root/boot
grub-install --root-directory=/mnt/root --recheck --no-floppy /dev/sda
umount /mnt/root/boot
umount /mnt/root
reboot