And my other squash (It's younger than the other one) and the lower leaves are getting yellow and start to dry on the plant.
Thanks!

I think these kind of things are really irritating, I hope you have sorted this out because it's going to be a big disaster for you.

Yeah that's what I'm trying to solve

The first picture suggests a fungus, perhaps powdery mildew. Second picture might be nitrogen deficiency or could be salt accumulation in the soil.

Any clues on how to solve those problems?

Re: your powdery mildew, check out the post from earlier this month on powdery mildew on squash. There were many suggestions posted.
Ralph