Posting a new update, if someone in the future has the same issues.
Even though a graphic screen was appearing in "Display settings" (a small 4:3 screen) as I said when pressing "Detect" is was not detecting. The Radeon Software was able to duplicate; but duplicate only not extend.
The trick was:
Pressing the Windows key + P and then choosing extend makes the screen work as an extention. Don't know why windows denies to make it work the other way but yes. Thank god it is solved.