Ford Ranger fuel problem

2002 ford ranger with 94,000 miles. 4cyl, 2.3l, 5-speed. I have never had a problem with it yet. I got into it today after letting it sit for 4 days. I went to start it and it would not kick over. It had plenty of fuel in the tank and was turning over just fine but would not start. After looking at a few obvious things I decided to crank the engine over for a little longer. It started to turn over after about 30 sec and then finnally started. It drove fine and I cant see why it didnt want to start. I went back about an hour later and it started fine. Any info will help. Thanks