Don't reset the PRAM. That's pointless. First check that Time Machine is turned ON in its preference pane, and that the backup destinations are still selected. If they are, please see below.
These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.
Launch the Console application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ Open LaunchPad and start typing the name.
The title of the Console window should be All Messages. If it isn't, select
SYSTEM LOG QUERIES ▹ All Messages
from the log list on the left. If you don't see that list, select
View ▹ Show Log List
from the menu bar at the top of the screen.
In the top right corner of the Console window, there's a search box labeled Filter. Enter the word "Starting" (without the quotes.) You should now see log messages with the words "Starting * backup," where * represents any of the words "automatic," "manual," or "standard."
Each message in the log begins with the date and time when it was entered. Note the timestamp of the last "Starting" message that corresponds to the beginning of an abnormal backup. Now
CLEAR THE WORD "Starting" FROM THE TEXT FIELD
so that all messages are showing, and scroll back in the log to the time you noted. Select the messages timestamped from then until the end of the backup, or the end of the log if that's not clear. Copy them to the Clipboard by pressing the key combination command-C. Paste into a reply to this message by pressing command-V.
If all you see are messages that contain the word "Starting," you didn't clear the text field.
The log contains a vast amount of information, almost all of which is irrelevant to solving any particular problem. When posting a log extract, be selective. Don't post more than is requested.
Please don't indiscriminately dump thousands of lines from the log into this discussion.
Please don't post screenshots of log messages—post the text.
Some private information, such as your name, may appear in the log. Anonymize before posting.
When you post the log extract, you might see an error message on the web page: "You have included content in your post that is not permitted," or "The message contains invalid characters." That's a bug in the forum software. Please post the text on Pastebin, then post a link here to the page you created.
