Is the driveway inclined? Check fuel level. Check all fuses and links. Check fuel delivery. Why did it stall? Are you sure it stalled and didn't just fail (stop because the motor stopped running)? The stock pump is very reliable -- is it the stock pump?
Does the starter whiiiirrrr but can't engage the flywheel? Try giving it a smart smack on the side with a soft mallet.
If you're under warranty and can't sort it out make a phone call.