Your file listing in post#6 shows that the /usr mountpoint is indeed missing.

So let's recreate it.

Boot from DVD:

Code:

ok> boot cdrom -s

When at # prompt:

Code:

# mount /dev/dsk/c1t0d0s0 /a

Code:

# cd /a
# mkdir usr

You can try rebooting now provided that was the only problem. Otherwise you should run fsck on the root filesystem to see what damage there is.

Code:

# umount /a
# fsck -n /dev/rdsk/c1t0d0s0

Note: Use the -n switch to ensure no modifiations to the filesystem initially until we know the extent of any damage.