Hi,
Both are quite correct.
"What happened to you?" is common and accepted.
"What has happened to you?" is cool, too.
The first one is an informal wh-question.
Something happened to you.
What happened to you?
Someone said it.
Who said it?
The only difference is the axiliary 'has' in the second one. It adds emphasis.
Josh: Something happened to my face?
Nomi: What happened?
Josh: Well...erm...
Nomi: What
HAS happened? Do tell!
Josh: I accidently walked into a tree. :?
Does that help?
For further infomation:
CLICK HERE