I have Dell Inspiron 1318 and it's been three years.

Now whenever I start my laptop, it runs for a while(It can be 5 min. to 1-2 hours) and then it get shut Off completely with no reason or blue screen.

I have checked the Fan and remove the dust from the heat sink but it keeps on switching off.

Is it a BIOS Issue or I need to replace motherboard?

Please help me with this. I need an expert advice.