I can't play this game, everytime I press Niva it doesn't open.
If you are using a mac(unless windows has this too) go to Finder and go to downloads. Find Niva and right click it. There should be an option to open. If you don't have finder go to downloads or wherever you saved Niva to and try to right click.
If this doesn't work I'm sorry. I'm no expert. This is just what i would try.