I fell to sleep while my car was running with the heater on. I didnt realise it was low on gas. I ran out . i put some in and it wont start

fuel covering the fuel pump is what keeps the pump cool.NEVER let the fuel level get that low!when the gas hand gets to 1/4 tank,consider that as empty,and go get more gas.it's possible the pump over heated and burned up? also consider yourself very fortunate that you woke up,because Carbon Monoxide is very mean!