System broke, Target sbin/init not found

[Vayu]

I shut down normally and upon the next boot my system was broken.  I get 
a root command line that has lost it's access to my hard disk.  I get 
the error message Target sbin/init not found.  I can't find sbin/init 
using ls, nor much of anything else like boot/grub or my home directory...

If I boot from a live CD I can mount the linux partition /dev/sda4 and 
see everything is there and looks intact.  It doesn't appear to be a 
hard drive failure.  I can still boot into windows.  As a matter of fact 
I installed the ext2 driver in windows and I can now access my data from 
windows.  (From there I can see sbin/init as well.)

I'm using Dapper, I did not do any kind of upgrades, it just happened 
out of the blue.

Any ideas on what is corrupt, and how I can get my system back without a 
re-install?