Contour won't start

I left my 1999 four cyl Ford Contour parked for several weeks. Now it won't start. Thinking that the trouble could've been caused by a faulty battery, I purchased a brand new one. But still it won't start. The engine cranks but doesn't start. I know that the problem is fuel related and not electrical because when I spray starting fluid into the air intake it does start for about 3 seconds. I changed the fuel filter but nothing. Somebody told me to try to keep the accelerator pedal depressed while cranking the engine. Today I tried that and the engine did start and ran for about 15 seconds, but then it died. When turning the ignition key on I can hear the fuel pump for about

2-3 seconds. The car ran very well until I parked it for about 5 weeks. Does anybody have a clue about what the problem may be and what I should check next? Many thanks in advance