Jeśli router się zawiesi, sygnał robi się słaby i nie mogę wysłać pliku.

Yes, the basic idea of zawiesić is to hang / suspend, but zawiesić się is also a very common expression for devices, programs, or systems that freeze, hang, or stop responding.

So here:

• router się zawiesi = the router freezes / crashes / hangs

This is a standard tech-related use in Polish.

Also, się is part of the verb here. You should learn it as a whole expression:

• zawiesić się = to freeze, to hang
• zawieszać się = to keep freezing / to freeze repeatedly

It does not mean the router is doing something to itself in a literal sense.

Because Polish often uses a perfective verb in its present form to talk about a future completed event after jeśli.

So:

• Jeśli router się zawiesi = If the router freezes / if the router should freeze
• literally the form looks present, but the meaning is future

This is very normal in Polish.

Compare:

• zawiesza się = is freezing / freezes regularly / keeps freezing
• zawiesi się = will freeze / freezes on a particular occasion

So in this sentence, zawiesi się fits because we mean a specific event that may happen.

This is mainly a question of aspect.

• zawiesić się = perfective
• zawieszać się = imperfective

In practice:

• Router się zawiesza. = The router freezes / keeps freezing / is freezing.
• Router się zawiesi. = The router will freeze / freezes at some future point.

Perfective verbs usually focus on a single completed event.
Imperfective verbs usually focus on the process, habit, or repetition.

So after jeśli, Polish often prefers the perfective form when talking about a future possible event.

Because robić się means to become / to get.

So:

• sygnał robi się słaby = the signal becomes weak / gets weak
• sygnał jest słaby = the signal is weak

That is an important difference.

In this sentence, the idea is that when the router freezes, the signal changes state and becomes weak. That is why robi się is more natural than jest.

A few similar examples:

• Robi się ciemno. = It’s getting dark.
• Robi się zimno. = It’s getting cold.
• On robi się nerwowy. = He’s becoming nervous.

Because słaby agrees with sygnał.

• sygnał is masculine singular
• so the adjective must also be masculine singular
• therefore: słaby

Compare:

• słaby sygnał = weak signal
• słaba sieć = weak network
• słabe połączenie = weak connection

The form changes according to the noun’s gender and number.

Polish can use to in if... then... sentences, but it is often omitted.

So both are possible:

• Jeśli router się zawiesi, sygnał robi się słaby...
• Jeśli router się zawiesi, to sygnał robi się słaby...

Both are natural.

Adding to can make the sentence feel a little clearer or more emphatic, but it is not required.

Because Polish usually drops subject pronouns when they are not needed.

The ending -ę in mogę already tells you the subject is I.

So:

• nie mogę = I can’t
• ja nie mogę = I can’t / I can’t

Adding ja usually gives emphasis, contrast, or emotional force.

For example:

• Nie mogę wysłać pliku. = I can’t send the file.
• Ja nie mogę wysłać pliku, ale on może. = I can’t send the file, but he can.

Because Polish often uses the present tense to describe a general result or a situation that regularly happens under certain conditions.

So this sentence feels like:

• Whenever / if the router freezes, the signal gets weak and I can’t send the file.

That is why nie mogę works well.

If you wanted to stress one specific future situation, you could also say:

• Jeśli router się zawiesi, sygnał zrobi się słaby i nie będę mógł wysłać pliku.

That means more clearly:

• If the router freezes, ... I won’t be able to send the file.

So:

• nie mogę = more general / describing what happens
• nie będę mógł = more explicitly future

Because wysłać is perfective, and here it means to send successfully / to get sent.

• wysłać = to send once, to complete the sending
• wysyłać = to be sending, to send repeatedly, to send in general

So:

• nie mogę wysłać pliku = I can’t send the file / I can’t get the file sent
• nie mogę wysyłać plików = I can’t send files / I’m unable to send files in general

In this sentence, the speaker is talking about one file and the inability to complete the action, so wysłać is the natural choice.

Because in standard Polish, the direct object often changes to the genitive after negation.

Compare:

• Mogę wysłać plik. = I can send the file.
• Nie mogę wysłać pliku. = I can’t send the file.

So:

• positive sentence: plik (accusative form, which looks like nominative here)
• negative sentence: pliku (genitive)

This is a very important Polish pattern.

You will see the same kind of contrast in many examples:

• Mam czas. = I have time.

• Nie mam czasu. = I don’t have time.

• Widzę samochód. = I see a car.
• Nie widzę samochodu. = I don’t see a car.

It is because of the negated verbal idea: nie mogę wysłać.

Even though móc is the finite verb, the object belongs semantically with wysłać, and under negation Polish normally uses the genitive:

• mogę wysłać plik
• nie mogę wysłać pliku

So for a learner, the simplest rule is:

• after a negated transitive verb idea, the object often becomes genitive

Because Jeśli router się zawiesi is a subordinate clause introduced by jeśli (if), and in Polish such clauses are normally separated by a comma.

So:

• Jeśli router się zawiesi, sygnał robi się słaby...

This is standard punctuation.

Yes. That is one of the most natural readings.

It can mean something like:

• If the router freezes, the signal gets weak and I can’t send the file.

In other words, this is describing what happens when that condition occurs.

That is why the mix of forms feels natural in Polish:

• jeśli ... zawiesi się = if it freezes
• robi się słaby = it gets weak
• nie mogę wysłać = I can’t send

The sentence is not necessarily about only one single future moment. It can also describe a typical consequence.

No, there are other possible ways, but they change the feel slightly.

For example:

• sygnał staje się słaby = the signal becomes weak
  
  • a bit more formal or neutral
• sygnał jest słaby = the signal is weak
  
  • describes the state, not the change
• sygnał słabnie = the signal weakens
  
  • more compact, a little more advanced

So robi się słaby is a very natural, everyday way to express the change.