Umarex Buckmark Lock Up

I AM dangerously new to this area of the forums and pray I won't wear out my welcome with incessant questions but I have another: my girlfriend has a Umarex Buckmark break barrel pistol that has been used as a trainer for her daughters over the past year or so. A few weeks ago it became inoperable as it will no longer lock up. To my question, is it fixable or expendable? My Google Fu has turned up nothing as yet and I am unfamiliar with air weapons in general.

My thanks again for your thoughts and assistance.