I know the ARES G36 has the fast spring change mechanism but If the rest of the takedown is the same as other G36s this will help
Airsoft G36 Take-Down/Disassembly Guide (EVIKE.COM) - YouTube
Also, my friend's ARES G36 came non functioning out of the box. I had to re-solder the wiring for him. Maybe you should take a look at that.
Can you also be more descriptive when you say it stopped firing? Do you hear clicks? Do you hear grinding? Do you hear nothing at all?