Ég var með of marga flipa opna, svo tölvan virkaði illa.

Literally, yes, að vera með is to be with, but in everyday Icelandic it very often means to have.

So:

Ég var með of marga flipa opna
= I had too many tabs open

This is a very common Icelandic way to express having something, especially in casual speech.

That is a very common learner question.

Normally, the preposition með does take the dative, as in:

með tölvu = with a computer

But in the expression vera með meaning have, it works differently. In practice, you should learn this as:

vera með + accusative

So in this sentence, flipa is not in the dative because this is the idiomatic have construction, not ordinary with.

No. Icelandic of here means too or overly.

So:

of marga flipa = too many tabs

This is completely unrelated to English of.

You will see of a lot in sentences like:

of heitt = too hot
of stór = too big
of margir = too many

Because both words are agreeing with the object, which is accusative plural masculine.

• flipi = tab
• accusative plural = flipa
• margur = many
• accusative plural masculine = marga

So:

of marga flipa = too many tabs

A useful comparison:

• margir flipar = many tabs nominative
• marga flipa = many tabs accusative

The sentence uses the accusative because of the vera með construction.

opna is agreeing with flipa and describes the state the tabs were in: they were open.

It is:

• masculine
• plural
• accusative

because it matches flipa.

So:

flipa opna = tabs open

This is a very natural Icelandic pattern when you mean have something open/closed/ready/etc.

Compare:

• opnir flipar = open tabs as a simple noun phrase
• vera með flipa opna = to have tabs open

So the adjective comes after the noun because it is describing the condition of the object in this construction.

It would probably be understood, but the original of marga flipa opna is more natural for the meaning I had too many tabs open.

There is a small difference in feel:

• opna flipa = open tabs as a noun phrase
• flipa opna = tabs open, focusing on the state they were in

With vera með, Icelandic often prefers the second pattern.

Because tölvan means the computer.

In Icelandic, the definite article is usually added to the end of the noun:

• tölva = a computer / computer
• tölvan = the computer

It is also in the nominative here because tölvan is the subject of the second clause:

tölvan virkaði illa = the computer worked badly

virkaði is the past tense of virka, which means to work, to function, or to operate.

So:

tölvan virkaði illa
= the computer worked poorly
= the computer wasn’t functioning well

It is about functioning, not about doing work in the sense of labor.

Because illa is an adverb, and it modifies the verb virkaði.

• illur / illt / illa are related forms
• illa = badly / poorly

Since the sentence is describing how the computer functioned, Icelandic uses the adverb:

virka illa = work badly / function poorly

Compare:

• illa modifies a verb
• an adjective such as illt would describe a noun or be used in a different structure

A very common pair is:

• virka vel = work well
• virka illa = work badly

Yes, this is normal and natural.

The sentence has two clauses:

1. Ég var með of marga flipa opna
2. svo tölvan virkaði illa

In the second clause, svo means so, and then you get the normal clause:

tölvan = subject
virkaði = verb
illa = adverb

So the structure is straightforward and idiomatic.

Not always. svo can mean different things depending on context, including so, then, and sometimes it has other discourse uses.

In this sentence, it clearly means:

so / therefore / as a result

So:

..., svo tölvan virkaði illa.
= ..., so the computer worked poorly.

That is the natural reading here.