How old is it.. ??
Gen 1 and Gen 2 are dying in droves now.. any that missed the 2year appointment with their maker have reached the end of the line.
Google search dead Time Capsule.. you will be dismayed at the number of people.. !!
Just to show even apple discussions has seen plenty of posts about the issue.. these are the two most active threads.. but there are literally hundreds of threads.
If you TC is a more recent one.. and still covered by warranty or you have applecare on any computer.. ring apple to arrange replacement if possible.