Hello, I've reinstalled the game recently, but when I start it, either as admin or normal, the game just start as a minimized window in a corner of the screen.
I can't move this window, and I can only interact with the "news", cause they are the only things I can see.

Anyone know how to solve this problem ?

I suspect that there is something wrong with the game resolution. In order to change the game settings you need to edit Windows registry (which is dangerous by the way, so beware!).
Game settings are stored into the registry entry HKEY_CURRENT_USER\Software\Obsidian Entertainment\Pillars of Eternity II\ and you should completely delete this entry: restarting the game afterwards should reinitialize all settings and hopefully solve the problem.