Where to lodge complains if not happy about Lenovo warranty problems?

My tablet is 6 months old but I was told that the problem it has is due to a cracked mother board and it is not covered with the warranty. No.1. I don't understand how a mother board gets cracked.
No.2. I don't understand why this kind of a problem because in my understanding the motherboard is the main component of the tablet.

Not the answer you were looking for?