Heard that old saves works on EE but when i choose new mission in chapter 3 screen goes black ?

Whoever told you that old saves work lied. They're incredibly buggy.

I know for a fact that starting the new quest on Roche's path leads to a black screen if your pre-EE save is already from chapter 3, and it's probably equally broken on Iorveth's path. That's in addition to several other issues that tend to pop up throughout the game when you use an old save (the Vergen wheel getting stuck comes to mind, as well as an issue where characters in the prologue can become invincible).

Unless you go back and play from an earlier save at the end of chapter 2, you won't be able to use your save for the new content. If you just want to play through the new content and don't have an earlier save from that point, I've posted saves here for both paths at the end of chapter 2. The bonus content works with both (each path has unique chapter 3 content).

there is a new patch out that fixes the vergen wheel

Yeah, and it was released something like an hour after my post.

The changelog specifies that it's for chapter 2, so chances are that OP is still stuck with a black screen unless they have earlier saves.