Genitive can be tricky. Along with obvious cases it can be used when:

a) the main verb is in negative -> Она не любит шума - She does not like noise
b) the verb refers only to the part of an object -> налить молока - to pour (some) milk
c) after certain verbs - просить, ждать, искать (and some others) -> Я ищу кота - I'm looking for a cat
d) after some verbs, that refer to fear and loss - бояться, лишаться, опасаться, etc. -> Он лишился сна - He lost his sleep