Key Won't Turn to "Start" Position

Major problem here.

My 1988 Eldorado - which I'm supposed to drive across the country this week - will not start.
The key will not turn past the "on" position in the ignition to the "start" position. The key stops dead in the "on" position; I physically can't turn the key any farther.

I've tried WD40, graphite lubricant, a new key and plenty of jiggling. Also tried shifting in and out of park, which I thought worked before, but to no avail this time.

Any suggestions? Thank you!