Learn Hardcore Greek: Ο υπολογιστής μου δεν λειτουργεί καλά σήμερα, μάλλον λόγω μιας μικρής καθυστέρησης στο ίντερνετ. - My computer is not functioning well today, probably because of a small delay on the internet.

This is the standard pattern: article + noun + possessive pronoun.
Putting μου before the noun (μου υπολογιστής) is wrong in modern Greek.

What is the difference between λειτουργεί and δουλεύει for “works”?

Both can translate as “works / is working”, but there is a nuance:

λειτουργεί = functions, operates (more neutral/technical; about a machine or system working properly)
δουλεύει = works (can be about a machine, but also about a person working at a job)

In this sentence, δεν λειτουργεί καλά focuses on the computer’s operation (how it functions).
You could also hear ο υπολογιστής μου δεν δουλεύει καλά, and it would still be natural, just a bit more casual.

Why is δεν placed before λειτουργεί?

In Greek, the basic rule is:
Negative particle (δεν / μη(ν)) + verb.

So you put δεν directly in front of the verb:

λειτουργεί → δεν λειτουργεί (does not work)
καταλαβαίνω → δεν καταλαβαίνω (I don’t understand)

You almost never put any other word between δεν and the verb, except weak object pronouns (e.g. δεν το ξέρω = I don’t know it).
So δεν λειτουργεί καλά is the normal word order.

Why is καλά used here instead of καλός?

καλός is an adjective (good), while καλά is the adverb (well).

καλός υπολογιστής = a good computer
λειτουργεί καλά = it functions well

Greek, like English, uses an adverb to describe how something happens:

English: works well, not works good
Greek: λειτουργεί καλά, not λειτουργεί καλός

What exactly does μάλλον mean here, and how strong is it?

μάλλον usually means probably, most likely. It shows that the speaker is not 100% sure, but thinks this is the most likely explanation.

In this sentence, μάλλον λόγω… = probably because of….
The degree of certainty is similar to English probably, sometimes close to I guess / I suppose depending on tone and context.

How does λόγω work grammatically, and why is it followed by μιας μικρής καθυστέρησης?

λόγω means because of / due to and it always takes a noun in the genitive case after it.

The basic noun is η καθυστέρηση (delay, lateness).
Genitive singular is της καθυστέρησης.

When you add an article and adjective in the genitive feminine singular:

μια μικρή καθυστέρηση (a small delay, nominative)
μιας μικρής καθυστέρησης (of a small delay, genitive)

So λόγω μιας μικρής καθυστέρησης literally is because of a small delay.

Why is it μιας μικρής καθυστέρησης and not μια μικρή καθυστέρηση?

The form changes because of the preposition λόγω.
Without λόγω, you’d say:

μια μικρή καθυστέρηση = a small delay (subject or direct object)

After λόγω, you must use the genitive, so all parts (article, adjective, noun) change to genitive feminine singular:

μιας (of a)
μικρής (of small)
καθυστέρησης (of delay)

That’s why you get λόγω μιας μικρής καθυστέρησης.

What is the gender and basic form of καθυστέρησης?

The noun is:

η καθυστέρηση (nominative singular, feminine) = delay, lateness, lag

The form καθυστέρησης is the genitive singular of the same noun: της καθυστέρησης.
In this sentence, καθυστέρησης is in the genitive because it follows λόγω.

Why is it στο ίντερνετ and not just σε ίντερνετ or something else?

στο is the contraction of σε (in, at, on) + το (the, neuter singular):

σε + το = στο

ίντερνετ is treated as a neuter noun in Greek, even though it’s indeclinable.
So you say:

στο ίντερνετ = on the internet / on the web

Using just σε ίντερνετ would sound incomplete or incorrect in standard Greek.

Is ίντερνετ the only way to say internet in Greek?

No. The two common options are:

το ίντερνετ – the most colloquial and widespread
το διαδίκτυο – more formal / standard Greek word (literally “network of networks”)

You can say:

λόγω μιας μικρής καθυστέρησης στο διαδίκτυο
(due to a small delay on the internet)

Both are correct; ίντερνετ feels more casual.

Can the word order in this sentence change? For example, can I start with σήμερα?

Yes, Greek word order is flexible, especially for adverbs like σήμερα (today).
All of these are natural, with slightly different emphasis:

Σήμερα ο υπολογιστής μου δεν λειτουργεί καλά, μάλλον λόγω μιας μικρής καθυστέρησης στο ίντερνετ.
Ο υπολογιστής μου σήμερα δεν λειτουργεί καλά, μάλλον λόγω μιας μικρής καθυστέρησης στο ίντερνετ.

The original order is very typical, but moving σήμερα is fine and often used to emphasize today.

Why is the present tense (λειτουργεί) used for “today”, not something like a continuous form?

Modern Greek does not distinguish between simple present and present continuous the way English does.
λειτουργεί can mean:

it works (in general)
it is working (right now / these days)

Context and time expressions like σήμερα (today) tell you it refers to what is happening today.
So δεν λειτουργεί καλά σήμερα = it’s not working well today.

What is the difference between υπολογιστής and κομπιούτερ?

Both can refer to a computer:

ο υπολογιστής – the standard Greek word (literally “calculator” / “computer”)
το κομπιούτερ – a loanword from English, colloquial

In everyday speech, people use both.
In more formal language (e.g. manuals, school, official texts), υπολογιστής is preferred.