Parallels wont switch from Mac OS to Windows

Plain and simple, I'm new at using Parallels. I recently switched my desktop background and since then, when I try to open up parallels, it wont switch from Mac OS to Windows, although the program indicates it has been activated. I don't know if using a new desktop background has anything remotely to do with this problem, but it is just what I witnessed. Anyone have any ideas what I may have done?

What do you mean by "switched your desktop background"? Are you referring to using "Spaces" or do you mean that you changed your wallpaper? Parallels should not be affected by a change of wallpaper or design, however, using Spaces is another matter.