The car would not start

start engine ? (jump leads) then with engine running disconnect battery terminal anyone ,then if engine stops its the altenator if engine keeps going then its the battery

Have you checked your spark plugs and wires? They may need to be replaced or the plugs may need to be cleaned or they may be gapped incorrectly.

When the engine warms up the engine computer goes into closed loop mode and relies primarily on the O2 sensors and the MAF sensor to calculate the correct fuel to air mixture - if one of the O2 sensors is fouled or the MAF sensor is not working properly, this can cause the problem.
Given the age of the car, I would also check the idle air control (IAC) and channels, the EGR valve and the throttle body for carbon buildup.

pull the spark plugs and see if water comes out of the cylinders. Disconnect the battery and turn it over by hand with the spark plugs removed.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

Ignition module or crankshaft postion sensor . Test it in the vehicle , test light , volt meter . Videos on youtube .
2004 Saturn Ion 2 2 Misfire Case Study P0300

Your alternator is bad. When the car drove home fine it was running off the battery and not the alternator. Replace the alternator, and the belt too while you're at it.

fuel pump quit

first,, had the engine stoped before you friend turned up, or did he stop it????
if you took the battery off has the car got a car alarm fitted to it if so, could it be the alarm immobiliser killing the feed to the starter??? also has the car ignishion kye got a chip in it to switch off the alarm? no chip no run like? and last have you put the battery on right and is it a good battery not a dud one

When you tur the key forward do you hear the fuel pump running? You should hear a low hum for about 20 seconds near the gas tank and then it stops. If you hear this your pump is good. If it keeps running or you can't hear it at all it's bad or the main fuel pump fuse is blown.

its your fulepump