in Time Machine what if it says The backup disk image “/Volumes/TimeMachine/Kevin’s iMac.sparsebundle” is already in use.
First, restart your iMac and Time Capsule. In most of the cases, this should solve that problem.
If it doesn't work, see > http://pondini.org/TM/C12.html
i am not using airport or time capsule
In that case, I suppose that you are backing up to a network drive, right? Try disconnecting it, and then, connect it again
Retrieving data ...