Not sure if this will help, but once it hits the wallpaper, try going to task manager, and see what is running under the processes list.
explorer.exe would be a good one to look for. If it is, try killing it, and restarting it (via new task, and typing in explorer).
If it isn't, try manually starting it. This will let you know if something is hanging up the desktop a bit...
Hope it helps.