Learn Russian: Громкий шум помешал мне спать. - The loud noise prevented me from sleeping.

The verb помешать (to hinder or prevent) requires the Dative case without a preposition. Even though English uses a direct object ("prevented me"), Russian treats this similarly to verbs of helping like помочь — the hindrance or help is directed to someone.

In English we say "prevented from sleeping". Why is there no preposition before спать?

Russian verbs of helping or hindering, like помешать, connect directly to the infinitive of the action. You don't need a preposition to say "from doing something" in this structure; it translates more literally as "hindered me to sleep."

Why is помешал perfective but спать is imperfective?

Помешал is perfective because the act of hindering was a single, completed event (the noise successfully kept you awake). Спать is imperfective because sleeping is an ongoing, continuous process that the noise interrupted.

The speaker says мне, so why does the verb помешал have a masculine ending? What if a woman is speaking?

The verb must agree with the subject of the sentence, not the object. The subject doing the action here is шум (noise), which is a masculine noun. Even if a woman is speaking, the verb remains помешал because the noise is what did the hindering.