Min mus fungerar inte, så jag måste använda tangentbordet hela dagen.

Because mus is a common-gender noun in Swedish (also called en-word).

• en mus = a mouse
• min mus = my mouse

Swedish possessives agree with the gender/number of the noun:

• min
  • common gender singular
• mitt
  • neuter singular
• mina
  • plural

So:

• min mus
• mitt tangentbord
• mina möss

Yes. Swedish uses mus for both meanings, just like English uses mouse for both.

Usually the context makes it clear:

• En mus springer i köket. = A mouse is running in the kitchen.
• Min mus fungerar inte. = My mouse isn’t working.

If needed, a speaker can make it more specific, for example:

• datormus = computer mouse

In a normal Swedish main clause, the negation inte usually comes after the finite verb.

So:

• Min mus fungerar inte.
• literally: My mouse works not

This is the normal Swedish word order in main clauses.

Compare:

• Jag förstår inte. = I do not understand.
• Han kommer inte. = He is not coming.

But in some subordinate clauses, inte comes before the verb:

• ... att musen inte fungerar = ... that the mouse is not working

So the short rule is:

• main clause: verb + inte
• subordinate clause: inte
  • verb

Yes. fungerar means works / functions.

The infinitive is fungera = to function, to work.

Examples:

• Datorn fungerar. = The computer works.
• Det fungerar inte. = It doesn’t work.

In everyday Swedish, people also often say funkar, which is more informal:

• Min mus funkar inte.

That means the same thing, but fungerar is a bit more neutral/standard.

Here så means so or therefore.

It connects the two ideas:

• Min mus fungerar inte = My mouse isn’t working
• så jag måste använda tangentbordet hela dagen = so I have to use the keyboard all day

So så is showing a result or consequence.

In other contexts, så can also mean other things, such as like this, then, or so/very, depending on the sentence. But here it is the conjunction so.

Because after måste you normally use the infinitive without att.

• måste använda = must use
• not måste att använda

This is similar to English, where we say must use, not must to use.

Other modal verbs in Swedish work the same way:

• Jag kan simma. = I can swim.
• Du vill gå. = You want to go.
• Vi ska äta. = We are going to eat.

So måste + infinitive is the correct pattern.

Yes. måste is the present-tense form of måste in modern usage, meaning must / have to.

So:

• jag måste = I must / I have to
• du måste = you must / you have to
• vi måste = we must / we have to

It does not change by person.

For past meaning, Swedish often uses var tvungen att instead of a simple past form of måste:

• Jag var tvungen att använda tangentbordet.
• = I had to use the keyboard.

That is very common and important for learners.

Because tangentbordet means the keyboard.

The base word is:

• ett tangentbord = a keyboard

To make it definite, Swedish usually adds the definite ending to the noun:

• tangentbordet = the keyboard

This is one of the most important Swedish patterns:

• en bok → boken
• ett hus → huset
• ett tangentbord → tangentbordet

So here the speaker means a specific keyboard: the keyboard.

It could be mitt tangentbord if you want to say my keyboard.

But this sentence says använda tangentbordet = use the keyboard, not my keyboard.

Both are grammatically possible, but they mean slightly different things:

• jag måste använda tangentbordet = I have to use the keyboard
• jag måste använda mitt tangentbord = I have to use my keyboard

The original sentence is just choosing the definite form, not the possessive form.

Hela dagen is the normal way to say all day.

• hela = whole / entire / all
• dagen = the day

Together, hela dagen means the whole day / all day.

This is a very common Swedish expression:

• hela dagen = all day
• hela veckan = all week
• hela natten = all night

Hela dag is not correct here.

You can also say hela dagen lång, which means something like all day long, but it is a bit more emphatic or stylistic.

That is just how Swedish builds this expression. Swedish often uses hela + definite noun for time spans:

• hela dagen = all day
• hela kvällen = all evening
• hela året = all year

So even though English does not use the, Swedish does.

This is a pattern worth memorizing as a chunk:

• hela dagen
• hela tiden
• hela veckan

The sentence has two main clauses joined by så:

1. Min mus fungerar inte
2. så jag måste använda tangentbordet hela dagen

If we label the parts:

• Min mus = subject
• fungerar = finite verb
• inte = negation

Then:

• jag = subject
• måste = finite verb
• använda = infinitive
• tangentbordet = object
• hela dagen = time expression

So the second clause is basically:

• jag måste använda tangentbordet hela dagen

That is a very typical Swedish sentence pattern.

Yes, absolutely. That is also correct.

There is a small difference in structure:

• ..., så jag måste ...
• ..., därför måste jag ...

With därför, Swedish follows the verb-second rule, so the verb comes before the subject:

• Därför måste jag ...
• not Därför jag måste ...

So these are both good:

• Min mus fungerar inte, så jag måste använda tangentbordet hela dagen.
• Min mus fungerar inte, därför måste jag använda tangentbordet hela dagen.

The second one can sound a little more formal or explicit.

In everyday spoken Swedish, jag is often pronounced more like yah.

So:

• jag måste often sounds roughly like yah MOSS-te

A careful or formal pronunciation closer to the spelling also exists, but learners will very often hear a reduced pronunciation in natural speech.

This is useful because many beginners expect the written g to be strongly pronounced, but in normal speech it often is not.

Använda means to use.

A rough pronunciation guide is something like:

• AHN-vend-a
  though exact pronunciation depends on accent.

In the sentence:

• måste använda = have to use

You do not need to break it into parts in order to use it correctly. It is best to learn it as a whole verb:

• använda datorn = use the computer
• använda musen = use the mouse
• använda tangentbordet = use the keyboard

Yes, but it would change the structure.

The original sentence starts with Min mus = my mouse.

If you had already mentioned the mouse and wanted to refer to it as the mouse, you could say:

• Musen fungerar inte. = The mouse isn’t working.

Or with a possessive plus noun, you normally do not use the definite ending:

• min mus
• not min musen

That is an important Swedish rule:

• min bok = my book
• not min boken

So in the original sentence, min mus is exactly right.

Here are the main noun forms:

• en mus = a mouse
• musen = the mouse
• möss = mice
• mössen = the mice

And:

• ett tangentbord = a keyboard
• tangentbordet = the keyboard
• tangentbord = keyboards
• tangentborden = the keyboards

This sentence is useful because it shows both noun genders:

• mus = common gender (en word)
• tangentbord = neuter (ett word)

That is why you get:

• min mus
• tangentbordet / mitt tangentbord