'99 Volks Jetta LS, 2.0 - Wont Start, Then Will Start.

Hello, as the subject line states I have a '99 Volks Jetta LS, 4 Door, 2.0. Engine code: AEG - Mileage: Almost 100,000

Lately I will start my car fine in the morning and head off to work. After I get off I will try to start my car and it will not start. The electronic stuff will turn on, and it will crank, but no start. I have to leave it sit for anywhere from 15 minutes to almost an hour and then try again, and it starts. (I have tried to repeat starting very so often and it wont, will only start after sitting for a few.) Why is this? Any ideas, help, or suggestions.

Here is some background info; the following has just been done/bought/replaced; Fuel Pump and Fuel Filter, New Battery, New Spark Plugs, New Serpentine Belt.