Не успела я открыть ноты, как учительница попросила начать сначала.

This is a very common Russian narrative pattern.

Не успела я открыть ноты, как ... means something like:

• Before I could open the sheet music, ...
• I hadn’t even had time to open the sheet music when ...
• sometimes, depending on context, No sooner had I ... than ...

So the structure не успел(а) X, как Y highlights that the second action happened almost immediately.

It is not just a simple logical negation. It often adds a feeling of suddenness or immediacy.

Because Russian past tense agrees with the gender of the subject in the singular.

Here the subject is я, and the speaker is female, so you get:

• я успела = I managed / I had time, said by a woman
• я успел = the same, said by a man

So:

• Не успела я открыть ноты... = said by a female speaker
• Не успел я открыть ноты... = said by a male speaker

Russian word order is much more flexible than English word order.

A more neutral version would be:

Я не успела открыть ноты, как...

But Не успела я... puts emphasis on the idea of hardly having time. It sounds a bit more expressive and natural in storytelling.

So the change in order does not change the basic meaning much, but it changes the focus and rhythm.

After успеть / не успеть, Russian usually uses a perfective infinitive when talking about managing to complete a single action.

• открыть = to open, as a completed act
• открывать = to be opening / to open repeatedly / to open in a process-oriented way

So:

• не успела открыть = did not have time to get it opened / before I could open it

That is the natural choice here, because the sentence is about whether the action could be completed before something else happened.

Успеть means to manage to do something in time, to have time to do something before a deadline or before something else happens.

So не успела открыть ноты does not simply mean I did not open the sheet music. It more specifically means:

• I didn’t have time to open the sheet music
• I wasn’t able to get to that action before the next event happened

That is why успеть is so common in situations where one action interrupts another.

Как does often mean how, but not in this sentence.

In the construction не успел(а) ..., как ..., как introduces the next event and means something like:

• when
• before
• and then immediately

So here it is part of a fixed pattern, not a question word.

This is why translating it word-for-word as how would be wrong in this sentence.

Ноты literally means notes, but in context it often refers to sheet music or the music score.

Russian commonly uses the plural ноты when talking about the written music a person is reading or playing from.

Compare:

• нота = a single musical note
• ноты = notes / sheet music

So открыть ноты means something like open the sheet music.

Good question. Russian often omits an object if it is obvious from context.

Учительница попросила начать сначала most naturally means:

The teacher asked me to start from the beginning

A fuller version would be:

Учительница попросила меня начать сначала

Here меня is omitted because it is easy to understand who the teacher is speaking to.

So the sentence is not incomplete; Russian simply leaves out predictable information more freely than English.

This is a normal Russian pattern:

попросить + кого-то + infinitive

meaning:

to ask someone to do something

So:

• попросила = asked
• начать = to begin

Together:

попросила начать = asked someone to begin

And with the implied object:

попросила меня начать = asked me to begin

This is very common in Russian with verbs like:

• просить / попросить = ask
• заставить = make
• велеть = order
• разрешить = allow

followed by an infinitive.

Because the teacher is asking for a single complete action: to start.

• начать = perfective, to begin once
• начинать = imperfective, to be beginning / to begin repeatedly / to begin in a general sense

In this sentence, the teacher is not talking about a repeated or ongoing process. She is telling the student to perform one specific action: start again from the beginning.

So начать is the natural choice.

They are different forms with different meanings.

Сначала as one word is an adverb meaning:

• at first
• from the beginning
• over again

In this sentence, it means from the beginning.

С начала as two words is usually a prepositional phrase meaning from the beginning of something, often followed by a noun:

• с начала урока = from the beginning of the lesson
• с начала года = from the beginning of the year

So here начать сначала means to start over / start from the beginning, and the one-word form is correct.

Because this sentence has two clauses:

• Не успела я открыть ноты
• как учительница попросила начать сначала

Each clause has its own finite verb, and как introduces the second clause in this fixed construction. Russian punctuation requires a comma here.

So the comma is not optional.

Yes, a little.

The pattern Не успела ..., как ... is perfectly normal Russian, but it has a slightly narrative, expressive feel. It is especially common in storytelling.

A plainer everyday version might be something like:

Я не успела открыть ноты, и тут учительница попросила начать сначала.

That means nearly the same thing, but the original sentence sounds more vivid and compact.