Friends g37

[Ensaner]

I was watching my friends g37, for a couple of days and when I was driving it the no key light popped up. (Every time I started the car it pops up, and always had problems locking/unlocking my car. I have to put the key directly next to the door to unlock it) then it happened again and the car just shut off then it wouldn't turn on, after trying and trying, I got it to turn on and the service engine light came on. I drove a little more than all the lights shut off[headlights, dash, center console] then the engine turned off so when I got it back on again the lights stayed off and said there was no key but I was able to get it back to home. The car is a 08 g37, and he just put a new battery in the key fob. Any ideas are appreciated.