I mean, the keys are fine and the screen shows up too hehe, but i can't change values on it.

Yes i'm at a multiplayer game.
But the arrow keys doesn't move from field or either change value of the first one (where it starts).

I'm at U30.

Can anyone help me?

Try pressing shift whilst pressing the arrow keys.

... Or was it control, alt or altgr

Go to Options > Controls and make sure to unassign all functions that are bound to any of the arrow keys.

Quote from Krane :

Try pressing shift whilst pressing the arrow keys.

... Or was it control, alt or altgr

Shift

Yep.
SHIFT did the trick.

Thanks a lot from this noobie