to commonly asked questions.

By Time Machine is not working.

Hey Scotty, my Mac has not backed up in 135 days. When I attached it ...I guess I hit the wrong button’s or something.

It may be time to start your Time Machine backup over again but first let’s try this:

With the backup drive plugged up, go into system preferences/Time Machine. Choose: Select backup disk. Choose: Add or Remove. Choose to remove the disk if it is currently listed. This will end the relationship with the drive if there was one. Next repeat the process but choose to Add. The should reestablish the relationship and the computer should begin backing up to the drive once again.
If that doesn’t work then there are a few possibilities.

1. The backup drive may not have enough space.
2. The drive may be failing/failed.
3. The drive may need to be reformatted and the backup drive started over again.
This image is a theme.plist hack