Replaced radiator in 2000 Subaru Outback, now engine won't crank after starting and running once.

I replaced the radiator in my manual
transmission 2000 Subaru Outback
because it was spewing coolant due
to a huge gash in the top of the old
one.  It was running fine prior, other
than that.  When I got it all put back
together, I started it and ran it for 15-
20 minutes to make sure there were
no other leaks, and that it wasn't
overheating. All fine.  Left my hood
up, and the key in the ignition in my
driveway (I live in a safe, suburban
neighborhood). Ran inside to get
ready for work, gone maybe 20
minutes. Came back out, turned the
key:  nothing. Not even a click.  Keep
in mind the car started and ran just
fine 20 minutes prior.  

After a week or so, on my next day
off, I took the battery to get it tested.
Turns out the battery was beyond
dead, so I get a new battery, put it in,
go to start the car and it makes a
bizarre electrical popping noise and
loses all power.  It does this every
time I open and shut the door, and
take the key out and then put it back
in and turn the ignition to try to start
it. What the heck is going on?