Sounds like what happens when you try to start the car with an
unprogrammed PATS key.  As an experiment, I tried to start my 2000
Focus with a new key after it had been duplicated on the key cutter,
but before it had been programmed.  I expected the starter motor to
turn but the computer to withold sparks, but what happened was
exactly nothing, the starter motor would not even crank.

I suspect either the chip in your PATS key may be interrmittently failing,
or there may be a loose connection to the telemetry coil surrounding the
ignition switch cylinder.  You might try using the 2nd key for a while
and see if the problem goes away, if so, you could be pretty sure it
was the key itself.

It sounds like there are some issues in common with my posting:

   I turned onto the on-ramp to get on the highway and the engine died
instantly.  There was no coughing or hesitation, it just stopped.
   I tried to restart it repeatedly, but didn't even get a click.  It was
like trying to start with it in gear.
   There were some other symptoms.  ALL of the panel lights normally
come on when you first turn on the ignition, but most of them go off
after 1-2 second.  In this case they all stayed on and the odometer
changed to "- - - - - " and nothing else seemed to work.
   I pushed the car well off the road and started fiddling to try to start
it.  It started immediately.
   Since that was a dangerous situation, I took it in to the dealer.  It
(of course ;>) didn't act up while in the shop, but they did the fuel pump
recall at no charge.
In the week since, it has stalled twice.  I was inching forward to back into
a parking stall when it died last night.  I tried several times to start it.
By the time I pushed it into the stall, it was back to normal again and
started repeatedly.
   I was a bit dubious about the "fuel pump module" recall because of the
anomalies in the instrument panel displays.
   I had an ignition switch problem about six months ago and ended up
having to  replace the steering column.  Since that time (whether or not
these are connected)
I have had several other "instrument cluster incidents" which did not result
in stalling.  The glitches were associated with the radio suddenly going
dead. That hardly qualifies as "life threatening", but again the problem
soon "fixed itself".  There was also an issue with the transponder keys
not working intermittently.
   Any ideas as to what the common factor is in all of these symptoms?

PS  If you have other RFID or transponder chips on your key ring,
they will BOTH be talking back at the time and can interfere with
each other.  It seems that this would affect starting, but not stalling.
I wrapped my key in aluminum foil to disable it to see if that
duplicated the symptoms.  It refused to start of course, but the
display remained normal.  I should try wraping the key AFTER
starting just to see if they periodically interrogate it.