A trivial question

This question may seem a little trivial but I am having trouble with a glitch in trying to set my desktop background (on XP). I had a picture there which I had opened using a photoshop program but when the program’s trial expired the picture vanished. the option to have a background is now frozen at none. Nothing else is affected. is there any simple way of correcting this problem because its an irritant? Tanx in advance