Dimension box disappear.

[igones]

I don't know why but my dimension box when drawing lines or whatever just disappear.

[Tom Beauford]

Dimension box? Do you mean dynamic input? F12 will toggle it on/off. It should also be a status toggle on your Drawing Status Bar at the bottom of your screen.

[jaberwok]

I don't know why but my dimension box when drawing lines or whatever just disappear.

Your image doesn't tell whether you are drawing lines or dimensioning.
You don't get a "dimension box" when drawing lines and you won't see it whilst dimensioning until after you place the second pick point.
Or, see Tom's answer.

[igones]

Yeahhh!! Dynamic Input. That's what i was looking for!

Thanks!