2002 Cadillac DeVille wont start, can't remove key from ignition.

I was driving the car home from work. I smelled a faint burnt electrical
smell. Shortly thereafter, my traction control light came on, then the alarm
system light, then my fuel gauge went to zero. After that, random warning
lights came on and went off. The fuel gauge showed the fuel level twice but
eventually pegged back to empty. I stopped the car to pick up my daughter
from school but when I turned the car off, the key would not rotate all the
way back in the lock cylinder to allow me to remove the key. The car will no
longer start. The key, while in its off position, was allowing some
accessories to run which eventually drained the battery. The car was towed
home and now on a battery charger with the positive lead detached. I'm
fairly handy with cars but complicated electrical systems escape me and I
don't know where to start with this one. I did pull the codes and came up
with a U1000 code as current. There were a couple of similar codes
marked as history but I didn't have anything to write with to jot them down.
Taking this to a shop is cost prohibitive for me so I'm hoping for something
here. Thanks in advance for any help you can offer.