I am having this problem with my time machine. My external hard drive is fine, there have been no changes in the past month to anything, except for running Onyx to do maintenance. However, this same problem occurred right before I used Onyx, backing things up. Whenever i plug it in, and I do a "back up now" it does it for only superficially for a few seconds. I know that due to podcasts and other data downloads that a backup cannot occur that fast. And in past cases it took at least a few minutes. Any thoughts?