Hello Randun,
Here's a few more things to check to hopefully help.
Normally you would delete the
NoChangingWallPaper DWROD, but 0 should work as well.
Check in the registry location below to make sure that there is not an
ActiveDesktop desktop key there.
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies
Make sure that your Windows is
activated. If it's not, and goes past it's trial period, you will get a black screen like this as well.