Why is my 97 honda accord turning over but wont start

we changed the valve covers and gave it a tune up put a new battery in. we found a lil oil in the spark plugs well it ran then cut off we started it up then it wouldnt start til we let it sit for a long while then it will start once and not again we also had the starter checked they said it was ok dont know wats wrong i can hear the fuel pump hum then cut off but we seem to b getting fuel but it wont start