impulse,
not = не
no = нет
nor = ни (in some cases)
I've noticed you still mix them up.

There are two big groups:
Что-то / кое-что, кто-то / кое-кто and нечто, некто -- refer to something and someone, an unknown specific object.
Что-нибудь, кто-нибудь, какой-нибудь etc -- refer to any- ... -thing/-one, so "-нибудь" part implies "any" or "some", a set of unknown objects you should browse to select the only one.
I hope it helps you do not mix these two groups.

The difference between the pairs: кое-что/кое-кто and что-то/кто-то
Кое-что случилось в Калифорнии... -- we know what exactly happened, so we used "кое-что".
Что-то случилось в Калифорнии... -- in fact, we don't know what really happened; we could hear that something occured, but we don't have exact information, so we used "что-то".
Кто-то напал на полицейского -- we don't know who attacked the cop, so we use "кто-то" (an unknown specific person).
Кое-кто напал на полицейского -- we know who this person is, so we're going to uncover him, or, on the contrary, we're going to hide this information (in this case "кое-кто" sounds like a hint).

About -нибудь words, I guess I could confuse you with "a set of objects" explanation. So I proceed with some examples.
Imagine that you are a witness. You saw how a criminal stole something. So now you are in the police station and you have to identify the criminal. You're looking at a few persons and a cop asks you (in perfect Russian):
- Кто-нибудь из этих людей вам знаком? Вы когда-нибудь видели кого-нибудь из них? Вы заметили какие-нибудь особые приметы преступника? На этих людях есть что-нибудь из одежды преступника?
Yes, in every sentence the cop offers you to select the right variant(s) from a set of the variants or reject all.