About 2 weeks when I had severe insomnia because of overtraining. I'd lay in bed every night for about 8 hours, but never fall asleep. It was frustrating as hell not being able to fall asleep, and the frustration only made the insomnia worse.
I finally got over it when I took some melatonin.

I was up three days in a row switching between playing Fallout 3, Retro Gaming Challenge, and various Virtual Console games.

Not much more than 24 hours for me. I have stayed up that long frequently though, to correct a forward rotating sleep cycle. Generally speaking, I never have insomnia.

You probably did sleep during that time without realizing it.

http://en.wikipedia.org/wiki/Microsleep

If you had literally gone 2 weeks without sleeping, that would actually be a new world record, as the current record is 11 days.