Solved system crash

Hello, my system FreeBSD 10.3 (i386) has just scrash, I do not know what to do, at the boot it stops at "Enter full pathname of shell or RETURN for /bin/sh:"; I have the command line prompt on this machine I have a Gnome installed, it refuses to load Gnome.
I have not been able to edit with " vi" the /etc/fstab. it is display in the /etc/fstab parameters to use a USB hard disk, here it indicates to me an error read-only.
On this computer I do not backup my c ++ programs!
it display: Mounting /etc/fstab filesystems failed, startup aborded!

I would like to be able to find my graphical environment

In single user mode the filesystems are mounted but mounted read-only.

For UFS:
fsck -y
mount -a -t ufs

For ZFS:
zfs set readonly=off zroot