i found a strange bug, when i'm fighting, and i press Z, a retangle appears and covers almost everything on the screen.
Thank you for the screenshot. Just to make sure we get the obvious stuff out of the way, Did you try restarting the application/updating your video drivers? (visual bugs are often fixed by video drivers, even though the game isnt too visually intensive)
Good to go. That box is actually caused by the main players sprite sheet, which your computer is rendering incorrectly for some reason.
Integrated graphics are never recommended for gaming.