two s dual boot

problem 1.Vista installed just fine but later when I restarted could not see desktop wallpaper. The screen is dead black and nothing I would allow me to change it. The only time I can see my desktop wallpaper is as the system shuts down.
Problem 2. Here it is two days after I install Vista as dual boot and suddenly when I booted into my default operating system (XP Home) I got the message that XP needed to be activated. The message included the information that there had been hardware changes that required activation. There have been no hardware changes since long before I installed XP. The only change has been the installation of Vista preimum.