Chosen Solution

Hi, I have connected a external drive to my iMac, formatted and I did the fist Time Machine Backup. As my internal HHD was working very slowly, i deactivated the Automatic Backup. Now, I have tried to Manually Backup but it did not work. It stay forever Preparing Backup——- I tried eliminating the backup in progress file ….. and rebooting, but it did not improved. Any solution? Thanks

Boot up holding down the Command and R keys then run Disk Utilities on your internal hard drive and see if you can repair it.