I' sorry, the problem is:
1. The laptop turns on but no sign on and off at 30 seconds, you hear working hdd and off.
2. Connect the power adapter and turn on only, no signs and off at 30 seconds!.
3. When you turn the fan does not work.
I think the notebook shuts down after 30 sec due to the high CPU temperature and this would be caused due to fan malfunction.
Sorry mate but it’s difficult to say what’s wrong here… I would say its motherboard related issue but you have replaced the motherboard too so this makes the issue more difficult…