La kablo ne konektiĝis; tial la modemo ne funkcias.

It breaks down like this:

• konekt- = the root meaning connect
• -iĝ- = a suffix meaning become / get into a state
• -is = past tense

So konektiĝis means that the subject became connected or got connected. In this sentence, with ne, it means that this did not happen.

Because konekti is normally transitive: someone or something connects something else.

For example:

• Mi konektis la kablon. = I connected the cable.

If you said La kablo konektis, it would sound like the cable connected something, which is probably not what you want.

By using -iĝ-, Esperanto makes the verb intransitive:

• La kablo konektiĝis. = The cable got connected.

So La kablo ne konektiĝis means the cable did not get connected / failed to connect.

Yes, and it is similar, but the nuance is a little different.

• La kablo ne konektiĝis focuses on the change of state not happening: it did not get connected.
• La kablo ne estis konektita focuses more on the state/result: it was not connected.

In many everyday situations, both are possible. The version with -iĝ- often feels more dynamic, as if the expected connection process failed.

Tial means for that reason, therefore, or that is why.

It is one of the Esperanto correlatives:

• kial = why / for what reason
• tial = for that reason
• ial = for some reason
• nenial = for no reason

So here tial links the two ideas logically: the cable did not get connected; therefore the modem does not work.

The semicolon joins two closely related independent clauses:

• La kablo ne konektiĝis
• tial la modemo ne funkcias

It shows a stronger break than a comma, but a closer link than a full stop.

A full stop would also be fine:

• La kablo ne konektiĝis. Tial la modemo ne funkcias.

The semicolon is just a neat way to show that the second clause follows directly from the first.

Because the sentence is talking about:

• a past event: the cable did not get connected
• a present result: the modem is not working now

So the tenses are chosen by the actual time of each action or state.

If you wanted to describe a situation entirely in the past, you could say:

• La kablo ne konektiĝis; tial la modemo ne funkciis.

That would mean the modem was not working at that past time.

La is the definite article, meaning the.

It is used because the sentence is talking about specific things: a particular cable and a particular modem, presumably the ones relevant in the situation.

Esperanto has:

• la = the
• no separate word for a/an

So:

• kablo can mean a cable or just cable in a general sense
• la kablo means the cable

Because in Esperanto, singular nouns normally end in -o.

So:

• kablo = cable
• modemo = modem

Even borrowed words are usually adapted to Esperanto noun endings. The root is modem-, and the noun form is modemo.

Related forms:

• modemoj = modems
• modemon = modem as a direct object

Because both nouns are subjects here, not direct objects.

In Esperanto, the -n ending usually marks the direct object.

Here:

• La kablo is the subject of ne konektiĝis
• la modemo is the subject of ne funkcias

So neither one takes -n.

Compare:

• Mi konektis la kablon. = I connected the cable.

There, kabon would be wrong—sorry, let's state it correctly: kabon is not the word; it should be kablon, with -n, because it is the direct object.

In Esperanto, ne usually comes directly before the word or phrase it negates.

So:

• ne konektiĝis = did not get connected
• ne funkcias = does not work / is not working

That is the normal and most straightforward placement. English speakers can usually think of it as similar to putting not with the verb phrase.

Yes, Esperanto word order is somewhat flexible, but this sentence uses the most neutral order:

• subject + ne
  • verb

So:

• La kablo ne konektiĝis; tial la modemo ne funkcias.

You could rearrange parts for emphasis, but that would sound more marked. For example:

• Tial la modemo ne funkcias.
• Ne konektiĝis la kablo...

Those are possible, but for learners, the standard order is best unless you have a reason to emphasize something.

A careful pronunciation would be roughly:

• La KA-blo ne ko-nek-TI-ĝis; TI-al la mo-DE-mo ne funk-TSI-as.

A few useful points:

• Stress in Esperanto is almost always on the second-to-last syllable.
• ĝ sounds like the s in measure.
• c sounds like ts, so funkcias has -tsi-.
• tial is pronounced ti-al, in two syllables.

So the main stresses are:

• KAblo
• konekTIĝis
• TIal
• moDEmo
• funkCIas