Hit 'a' to frame all the curves. It's probably just a change of the view in the graph editor. If it's a matter of the animation actually changing, not sure how that could have happened, unless you scaled all the keys way down.
SimplyMaya specialises in Maya tutorials. We offer over 1,000 individual Maya training videos, ranging from basic Maya tutorials through to intermediate Maya tutorials. Our tutorials are created by instructors with industry experience and are designed to get you up and running in Maya quickly without making it seem like hard work.