99.5 Jetta TDI won't start

Recently my 99.5 Jetta TDI has been having a hard time starting. It starts just fine when it is cool however, if I am driving to several places and when I get to each destination I turn the engine off for periods of 5- 10 minutes, eventually it won't start. The engine will turn over, but doesn't seem to catch. If I let it sit for another 10 minutes it will start. After it started acting up the first time, I replaced the fuel filter and pulled off the fuel shut off valve to see if it was working (it was) but it still continues to do the same thing. Once it wouldn't start so after about 15 min, I was able to get it to start, and a quarter mile down the road at a stop sign, it died once again. I walked home and picked up the car about 30 minutes later and presto, it fired up and I drove it home. When it is running, it runs fine. Has anyone else had an experience like that? Does anyone have any suggestions on what to do next? My wife is planing on taking the car on a trip this saturday but I don't want it to leave her stranded somewhere. Any suggestions would be most helpful. Thanks