Hers: 1999 Kia Sephia .... mine: 1984 Mercedes 300D turbo diesel
As mentioned upthread, give her (the Kia not your wife) a shot of ether.
If it fires, probably the fuel pump, especially if no “check engine” light is on.
Kia - probably fuel filter, but a 99 could be fuel pump. Lot easier to change the filter for first try.
The Benz - try WD-40 into the ignition switch then giggle the key, might free it up.
Might see if Autozone or one of the other places that sells parts has a diagnostics machine to do a free check on the computer system of the KIA. The Merc sounds like something just got old with the ignition - shouldn’t be too tough/expensive if that’s the only issue.