故障って英語でなんて言うの？

I used these three different answers, because this is what we say in a common and natural conversation. For example if my computer broke then I would explain to the computer technician that "it isn't working anymore", "it won't power/come on at all", or "it probably stopped working.

I dropped my smartphone and the screen's shattered. It has also stopped working. My car battery is dead. (My car has broken down). I dropped my camera into water and now it doesn't turn on. I dropped my laptop this morning and it is not functioning well now.

The phrase 'break down' functions both as a noun and a phrasal verb. In this context, it has been used as a phrasal verb and it means 'to stop working (of a piece of equipment)'. So, when referring to a computer, you may say: My computer has broken down. In this case, the past participle tense of the verb to 'break' has been used, 'has broken'. The verb to'crash' has several meanings, but, in this context, it means '(of a computer, computing system, or software) fail suddenly'. So, you may say: My computer has crashed. This phrasal verb 'break down' can also be applied to a car or any machine that has stopped working. So, you may say: My car has broken down.

example "i cannot use my computer, it malfunctioned last night". or "my computer broke down". or "my car broke down". or "i can't use my phone. It has broken".

The most common and casual way to say it would be to say that it has 'stopped working'. This can be used for all objects, manual and electrical etc. 'Broken down' is mostly used for electrical items, and specifically cars. 'Malfunction' is almost always used for computers and electronic items that have stopped working.

To give up the ghost = To quit; to cease functioning. "My old computer finally gave up the ghost the other day." To pack up = This is an informal, British expression - if a machine or piece of equipment packs up, it stops working "The camera packed up after I dropped it in the sea." To bite the dust = be killed, expire, die, pass away/on, expire, decease, perish, depart this life, be no more, breathe one's last, draw one's last breath, meet one's end, meet one's death, meet one's Maker, give up the ghost, go to the great beyond, cross the great divide "The baddies bite the dust with lead in their bellies."

*I broke my computer. The definition of broken is split, out of order, or not continuous. An example of broken used as an adjective is the phrase "a broken home," which means a home where the father and mother are not living together. An example of broken used as an adjective is the phrase "broken watch," which means a watch that is not keeping accurate time. Therefore if your computer breaks it means that you dropped it and broke your computer screen.