has / is confusion

[Tekoyla]

What's happened to you ?
means What has happened to you ? or What is happened to you ?
OR
The ground's frozen.
The ground is frozen or the ground has frozen ?

and if the sentence with the is, is incorrect is that a rule that you can't put past simple after "is" then ?

[Alan]

Hi,

[Tekoyla]

[Beeesneees]

I think you are trying to match 'have' to 'you', but it doesn't work that way.
Turn the question into a statement, and you'll find that 'has' matches a third person singular subject
What has happened to you?
It (or a noun) has happened to you.
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Cheers m' dears!