Corrupt 12.04 automatic update

[Joe Bissett]

I am a complete Ubuntu newbie.  My wife uses the old networked machine 
for e-mail and internet.

A week or so ago an automatic update from 11.10 to 12.04 was offered, 
and I accepted.  Something in the process got corrupted, and although 
the system now loads, shortly after the desktop appears, an error 
message pops up "System program problem detected".  The option to 
"Report problem" is greyed out.  Clicking "Cancel", or the (X) only 
starts a loop of messages, eventually ending in a reboot.  I can see via 
the menu that updates are available, and I can bring up the menu, but I 
can not successfully install the updates.

This morning while stumbling around, I finally received a meaningful 
error message:

"The application Unity 2D Panel has closed unexpectedly"
"/usr/bin/unity-2d-panel"

I know that I can use terminal to enter commands, etc., as I have done 
that in the past, following explicit instructions.

Also, I have downloaded the 701MB iso file for x86 and could probably do 
a new install; however, there should be a way to fix the problem with 
the existing installation.

Any help will be appreciated.  Thanks in advance.

Joe Bissett