What could be the problem and what should I do?

My macbook is not responding (freezing), it happened twice in about 2 weeks, if i force turn it off, It won't turn back on.

I've tried everything on the internet like to press Control + Shift, etc methods but nothing came out of it. The macbook has never behaved like this before, only these past two weeks. Before i'd switch it off and on without any problem, and it would respond very well.

Please help!