Við getum ekki notað netið þegar rafmagnsleysi verður.

Við means we, and getum is the 1st person plural form of the verb geta (can / be able to).

So:

• ég get = I can
• þú getur = you can
• hann/hún/það getur = he/she/it can
• við getum = we can
• þið getið = you all can
• þeir/þær/þau geta = they can

Because the subject is við (we), the verb has to be getum.

In Icelandic, ekki (not) usually comes after the finite verb in a main clause.

So:

• Við getum ekki ... = We cannot ...

This is very normal Icelandic word order. Compare:

• Ég skil ekki. = I do not understand.
• Hún kemur ekki. = She is not coming.

So in your sentence, getum is the conjugated verb, and ekki follows it.

Netið is the definite form of net.

• net = net / network / internet
• netið = the net / the internet

In Icelandic, the definite article is usually added to the end of the noun instead of being a separate word like English the.

So:

• net = internet
• netið = the internet

After nota (to use), the object is in the accusative case, and for this neuter noun, the definite accusative singular form is netið.

Yes, in this sentence netið is naturally understood as the internet.

Although net can literally mean net or network, in everyday modern Icelandic netið very often means the internet, just like English speakers say the internet.

So notað netið means use the internet.

Notað is the supine/past participle form used with geta in this construction.

The verb is nota = to use.

After modal verbs like geta (can), Icelandic often uses the infinitive or a related verbal form depending on the structure. In this sentence, notað functions as the non-finite verb meaning use.

So:

• Við getum ... notað netið = We can ... use the internet

For a learner, the important thing is to recognize geta notað as a common pattern meaning can use.

Þegar means when in this sentence.

So:

• þegar rafmagnsleysi verður = when a power outage happens

Be aware that þegar can also mean already in other contexts, so you have to tell from the sentence which meaning it has.

Examples:

• Ég fer þegar heim. = I’m going home now/immediately.
• Þegar hann kemur, förum við. = When he comes, we leave.

Here it clearly means when because it introduces a time clause.

Icelandic often makes compound nouns, and rafmagnsleysi is a good example.

It breaks down like this:

• rafmagn = electricity
• -leysi = lack / absence / without-ness

So rafmagnsleysi literally means lack of electricity, i.e. a power outage / power failure.

This kind of word-building is very common in Icelandic, and learning to spot the parts can help a lot with vocabulary.

Because the sentence is talking about power outages in general, not the specific power outage.

• rafmagnsleysi = a power outage / power failure / power outage in general
• rafmagnsleysið = the power outage

In a sentence like this, Icelandic often uses the indefinite form where English might also say a power outage or just power outages in general.

So:

• þegar rafmagnsleysi verður = when there is a power outage / when a power outage occurs

Verður is a form of the verb verða, which often means become, but it can also mean happen, occur, or take place, depending on context.

Here, it means something like:

• occurs
• happens
• comes about

So:

• rafmagnsleysi verður = a power outage happens / occurs

This is a very common Icelandic use of verða.

Because the subject of that clause is rafmagnsleysi, which is a singular noun.

The clause is:

• þegar rafmagnsleysi verður

Since rafmagnsleysi is singular, the verb is also singular:

• rafmagnsleysi verður = a power outage occurs

If the subject were plural, the verb form would change accordingly.

Yes. You can also say:

• Þegar rafmagnsleysi verður getum við ekki notað netið.

That means the same thing: When a power outage occurs, we cannot use the internet.

But notice something important: Icelandic tends to keep the finite verb in second position in the main clause. So when the time clause comes first, the next part is:

• getum við not
• við getum

That word order is very important in Icelandic.

A useful breakdown is:

• Við = we
• getum ekki = cannot
• notað netið = use the internet
• þegar = when
• rafmagnsleysi verður = a power outage occurs

So the structure is basically:

We cannot use the internet when a power outage occurs.

That is a very natural Icelandic sentence with:

1. a main clause: Við getum ekki notað netið
2. a subordinate time clause: þegar rafmagnsleysi verður