I had just learned how to do a backhand spring and 2 days after I was doing it and I just had a mental block and I couldn't do it anymore. How can I over come my fear?

Do you have spotters that you trust to help you? Sometimes it is just a matter of making yourself go for it. Remind yourself that you already know what to do, and picture it in your mind.

Is there anyone that you could show how to do one? Sometimes being the one to teach someone else can help as you are more focused on making sure that they know what to do and what it should look like.

What does your block involve? -- fear of falling flat? Fear of crashing into something? Fear of being unable to complete the spring? Make sure the way is clear, use mats to cushion the springing space (during practice), and like Doula suggested, use spotters.