Si el ratolí no funciona, no puc obrir l'arxiu.

Si means if. This is a conditional sentence: one thing depends on another.

In this sentence, Catalan uses si + present indicative for a real or possible situation:

Si el ratolí no funciona, no puc obrir l'arxiu.

That is the normal pattern for everyday conditions like this. You do not use the subjunctive after si here.

El is the masculine singular definite article, meaning the.

Catalan usually keeps the article with nouns in places where English sometimes leaves it out. Here, el ratolí means the mouse, referring to the specific mouse being used.

So ratolí by itself would usually sound incomplete in this sentence.

Yes. Ratolí is the normal Catalan word for both the animal mouse and the computer mouse, just like in English.

The context makes the meaning clear. Since the sentence talks about opening a file, it obviously means the computer mouse.

Because each clause has its own negative verb.

• no funciona = does not work
• no puc obrir = I cannot open

Catalan puts no directly before the verb each time you want to negate it. So if both parts are negative, you use no in both parts.

Puc means I can or I am able to.

It is the first person singular present form of poder, meaning to be able to / can.

So:

• puc = I can
• pots = you can
• pot = he/she/it can

In this sentence, no puc obrir means I can't open.

Because after poder, Catalan uses the infinitive directly.

So you say:

• puc obrir = I can open
• puc fer = I can do
• puc venir = I can come

There is no extra word corresponding to English to in this structure.

Because arxiu begins with a vowel sound, the article el becomes l'.

So:

• el + arxiu → l'arxiu

This apostrophe is very common in Catalan. It works much like contraction for smoother pronunciation.

Yes. Arxiu is a normal and standard word for file in computing.

So obrir l'arxiu is a natural way to say open the file.

Depending on context, arxiu can also mean archive, but in a sentence like this, file is the natural interpretation.

A simple English-friendly approximation is:

• ratolí → rah-toh-LEE
• arxiu → ar-SHEEW

A few useful pronunciation points:

• The accent in ratolí shows the stress is on the last syllable: ra-to-LÍ
• The x in arxiu is pronounced like sh

Exact pronunciation varies a bit by dialect, but those approximations are good enough for a learner.

Yes, that is also correct.

Both of these are natural:

• Si el ratolí no funciona, no puc obrir l'arxiu.
• Si no funciona el ratolí, no puc obrir l'arxiu.

The version with el ratolí before the verb is a very neutral word order. The version with no funciona first can put slightly more focus on the fact that it is not working.

Because the conditional clause comes first.

When the sentence starts with a si clause, Catalan normally separates it from the main clause with a comma:

Si el ratolí no funciona, no puc obrir l'arxiu.

If you reversed the order, the comma is often left out:

No puc obrir l'arxiu si el ratolí no funciona.

Yes. Funcionar is the standard verb for saying that a machine, device, system, or program works or functions.

So el ratolí no funciona is completely natural.

In more informal speech, you may also hear no va for devices, but no funciona is very clear and standard.