Ef skjávarpinn virkar enn ekki, þurfum við að skipta honum út.

Because Icelandic usually attaches the definite article to the end of the noun.

• skjávarpi = a projector
• skjávarpinn = the projector

Here it is definite because the sentence is talking about a specific projector, not just any projector.

Ef means if. It introduces a conditional subordinate clause:

• Ef skjávarpinn virkar enn ekki = If the projector still doesn’t work

So the sentence sets up a condition first, then gives the result or necessary action.

Virkar is the present tense, 3rd person singular form of virka, which means to work, to function, or to operate.

It is singular because the subject is singular:

• skjávarpinn = the projector
• therefore: skjávarpinn virkar = the projector works

Enn ekki means still not.

So:

• virkar enn ekki = still doesn’t work

A learner may notice that Icelandic often uses enn in places where English uses still or yet, depending on context.

This is because of the Icelandic V2 rule in main clauses.

When the sentence begins with another element—in this case the if-clause—the finite verb of the main clause comes next, before the subject:

• Ef ..., þurfum við ...

If you said the main clause by itself, it would normally be:

• Við þurfum að skipta honum út.

So the fronted conditional clause causes the word order change.

Because þurfa is normally followed by að + infinitive.

So:

• þurfa að skipta út = need to replace
• þurfum við að skipta honum út = we need to replace it

This is very common in Icelandic:

• Ég þarf að fara = I need to go
• Við þurfum að bíða = We need to wait

It means to replace, to swap out, or to change out.

The important thing is that this is a multi-word expression:

• skipta út e-u = replace something

The particle út is part of the meaning, not just an optional extra word.
Without út, skipta can mean things like divide, share, exchange, or change, depending on context.

Because Icelandic often separates a verb from its particle in actual sentences.

The dictionary form is:

• að skipta út

But when there is an object, it often goes in between:

• að skipta honum út

That is very similar to English swap it out or change it out.

Because skipta út takes the dative case, not the accusative.

So the pronoun referring back to skjávarpinn has to be dative:

• nominative: hann
• accusative: hann
• dative: honum

Since skjávarpinn is masculine, the pronoun is masculine too, and because of the verb expression it appears in the dative: honum.

In Icelandic, pronouns agree with the noun they refer to in gender and also appear in whatever case the grammar requires.

• skjávarpinn is masculine singular
• so the pronoun referring to it is masculine singular
• after skipta út, that pronoun must be dative
• therefore: honum

So honum here means it, referring to the projector, even though the form is grammatically masculine.

Because subordinate clauses introduced by ef normally have straightforward clause order, with the subject before the verb unless something else is being emphasized.

So the neutral pattern is:

• Ef skjávarpinn virkar ekki ...

This is different from the main clause, where Icelandic follows the V2 pattern.

Yes, but the meaning would change.

• skjávarpi = a projector
• skjávarpinn = the projector

So:

• Ef skjávarpi virkar enn ekki ... would sound more like If a projector still doesn’t work ...
• Ef skjávarpinn virkar enn ekki ... means a specific, known projector

In this sentence, the definite form is the natural choice.