New Head, everything almost right but...

Ok so the new head on my BMW is installed, its a 1996 328is. it hasn't been running for a couple of months since I was away at uni while my father was taking care of getting it fixed and took it to a mechanic. Everything has been reinstalled other than the cooling system(i.e. no pipes just the thermostat and waterpump are on there). So the mechanic tried to start her up just to make sure she would turn on before putting the cooling system components back on there. She cranks and everything just fine, and at first we thought she wasn't getting fuel pressure, but the mechanic went over everything and checked to see if the fuel pump was bad or there was a bad relay etc. and as it turns out the fuel pressure was fine, but when he tried to scan the cars computer it would not work(his english is bad so I'm not exactly sure what he meant). He said that the ECU had to be reset and that was the reason the car was not starting despite having fuel pressure, oil, and cranking fine. Does this make any sense? and if so how do I reset the computer? I asked my friend who used to drive an A4 Audi and he said to completely remove the batery and put it back in. Someone help me, my car is soo close to being finished and I really cannot take the **** anymore

to clarify the car starts puttering a little when its cranked but never fully starts. The mechanic says he cannot get his obd2 scanner to read the codes and he says the fuel pump is fine. Check engine light is indeed on.