Two days ago I bought a well-maintained 2001 QX4 with 104,000. Next morning the car wouldn't start. The starter engaged but, for an hour, the car would not start. Finally, after I went to work my wife got it started. Since then the same thing has happened a couple times.
The red security light flashes as I try to start it. Is that normal or does it indicate a problem with the security system? Is there maybe a fuel cutoff in the security system? I'm pretty sure it has the standard security system.

It did turn out to be a key issue. One key was programmed and one was not. The 'bad' key allowed the starter to crank but wouldn't let it start.