Question Can using a cracked laptop screen hurt my laptop?

Do not worry about it. The only issue you may face is the crack getting bigger, although I'm not sure how usable it would be with a crack that large.

With regards to this weird mercury thing, the mercury in the LCD's is so little its practically nothing.
I've used a laptop with a cracked screen for over 5 years, and I do not seem to suffer Mercury poisoning.