Won't start after being on hill

Hi,
Got a 99 1.0l auto. Left it parked on a hill with nose higher than tale. There wasn't much fuel in tank. First time turned key, it started and died after 2 seconds. I let it roll down to flat surfAce. Tried again after a day and did same thing, started and died, then wouldn't start again. Turns over fine with battery and tried jump starting. Open fuel can and a big air release sound. Put gallon of petrol in but stilt won't start.
Any ideas?
Thanks a lot

Fuel filter blockage?
Maybe let the fuel pump prime for about 10sec then try starting it.
Pull the plugs out and check if they're wet/flooded.