System Switched Off

Forumers please help me out. My system suddenly switched off while i was reading and refused to come on till after some time, it came on but went off again after some minutes severally untill it finally went off till now. It has refused to come on uptill this post. I took it to an Engineer who said it was Motherboard problem while another said it was processor problem. Please what is wrong with my system. I have so much vital documents in it that i cant afford to lose them. Please help me. Thank you for all your support so far. God bless you all.