kono kaban ni ha nootopasokon ga hairimasen.

に marks the destination or container with the verb 入る: something goes into the bag.

Adding は after に makes that whole phrase the topic: as for in this bag / in this bag, ...

So:

• このかばんにノートパソコンが入りません。 = a more neutral statement
• このかばんにはノートパソコンが入りません。 = puts focus on this bag, often with a slight contrast such as in this bag, a laptop won’t fit

That は often sounds like there may be other bags where it would fit.

Because 入る is an intransitive verb.

With 入る, the thing that goes in or fits is treated as the subject, so it takes が:

• ノートパソコンが入る = the laptop fits / goes in

English often uses an object in this kind of idea, but Japanese does not here.

If you use the transitive verb 入れる meaning to put in, then you would use を:

• ノートパソコンをかばんに入れる = to put the laptop into the bag

So in your sentence, the laptop is not a direct object; it is the thing that does or does not fit.

入りません is the polite negative form of 入ります, from the dictionary form 入る.

In this sentence, it literally means something like:

• does not go in
• does not enter

But in natural English, the best translation is usually:

• doesn’t fit
• won’t fit

So the sentence is talking about the laptop not being able to go into the bag, usually because of size or lack of space.

This is a very common learner question because 入る ends in -る, but it is not an ichidan verb.

It is a godan verb.

The pattern is:

• dictionary form: 入る
• polite form: 入ります
• polite negative: 入りません

So the る changes to り before ます.

This is important because beginners often expect all -る verbs to behave like ichidan verbs, but 入る does not.

Because に marks a destination or endpoint, and with 入る, the bag is the container something goes into.

• かばんに入る = to go into a bag

By contrast, で marks the place where an action happens.

So で would not be the normal particle here, because the sentence is not about doing an action at the bag; it is about something entering into the bag.

They do different jobs.

• は marks the topic: what the sentence is about
• が marks the grammatical subject of the verb

In this sentence:

• このかばんには = as for this bag / in this bag
• ノートパソコンが = the laptop is the thing that does or does not fit

So the sentence has:

• a topic: the bag
• a subject: the laptop

That is very normal in Japanese.

Yes, often it does.

このかばんには can sound like:

• in this bag, a laptop won’t fit
• as for this bag, a laptop won’t fit

That can imply something like:

• maybe it fits in another bag
• maybe other things fit in this bag, but not a laptop

The contrast is often mild, not dramatic. Whether it feels strongly contrastive depends on context and intonation.

They come from different verbs.

• 入る = to go in / to fit
  
  • 入りません = doesn’t go in / doesn’t fit
• 入れる = to put in
  • 入れません = do not put in / will not put in in standard grammar

So:

• ノートパソコンが入りません = the laptop won’t fit
• ノートパソコンを入れません = I won’t put in the laptop or I do not put in the laptop

If you want to say cannot put in, standard Japanese would usually use 入れられません.

Yes, to some extent. Japanese word order is flexible as long as the particles stay clear.

For example:

• このかばんにはノートパソコンが入りません。
  Neutral and natural
• ノートパソコンはこのかばんには入りません。
  As for a laptop, it won’t fit in this bag
• このかばんには、ノートパソコンは入りません。
  Stronger contrast on laptop; maybe other things do fit

So you can move things around, but the nuance changes depending on what you make the topic.

No. Standard Japanese is normally written without spaces.

This sentence would usually be written as:

このかばんにはノートパソコンが入りません。

The spaces are often added in textbooks or beginner materials to make the sentence easier to read.

The casual plain negative form is:

このかばんにはノートパソコンが入らない。

That is the plain-form equivalent of 入りません.

So:

• polite: このかばんにはノートパソコンが入りません。
• casual: このかばんにはノートパソコンが入らない。

Both mean the same basic thing; the difference is politeness and style.