They all mean what happened. But what's the difference in between? Feel free to add examples. Thanks!
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The only difference is in the formality levels. All four phrases mean "What happened?" or "What's wrong?", depending on the context.
To put the four phrases in the order of formality, we will have:
Is 1) very formal then? No, it is not because it uses 「する」, which is not very formal at all. More formal than 1) would include:
「いかが」 is more formal than 「どう」. In my experience, very few Japanese-learners can use freely and correctly the formal versions of the wh-words. Since 「いかが」 is formal, it is not to be used with 3) and 4) above. You will sound more than weird if you do, I promise.
If you are an adult speaker talking to another (a stranger) on the street, you would probably use any of the phrases listed above (including the two I added) except for 「どうしたの」 and 「どうした」.
You can use 「どうしたの」 and 「どうした」 when talking to (close) friends, your own students, kids (either your own or strangers'), etc. The slight difference between those two is the fact that the former sounds a little softer than the latter.
Finally, absolutely none of the phrases we discussed above are gender-specific. There seems to exist much misunderstanding among J-learners regarding the sentence-enders such as 「の」, 「わ」, etc.
Well the last one is just the polite form. The first one, の, is a casual question marker, mostly used by women. のです you can find literally dozens of discussions and explanations about that all over the internet. It's just emphasis or it makes it sound like the person is "pressing" for an answer.