back up fails every time

Hi guy's I have an extra harddisk what I want to use for back up, and everytime I start back up in the beginning no problem but then about 35-40% into the back up it stops.

How can I fix this?

See the  details at the bottum.

Please I am a novice in this.

Microsoft Product: Windows Operating System;
Version: 6.1.7600.16385; Event ID: 754; Event Source: Microsoft-Windows-Backup;