Evan is correct, it could be a ton of things. Evan has only been in RC since it was invented so he has seen it all. I remember when I was first learning to fly heli's that I had a Concept .30 get away from me. I reality it was a gust of wind that balooned it up and away from me. I did not have neg pitch set at that time because I was just learning. It was very hard to get back down so I just let it fly a few circuits around the field trying figure how to get it down. I crashed also and rolled it down the runway. Great crash though!! After my first lesson in forward flight I programed in -3 degrees of pitch in hover mode . I also felt that I had a glitch. I went on to repair the bird and used the same radio for several years with out a problem. Bottom line is to think out of the box and be brave enough to test it.

Jim