Hi FACE211, welcome to GTG!
Almost always when a computer refuses to complete defragmenting it's because of a program running in the background. Every time that program writes to the hard drive defrag has to restart.
You can restart your computer in safe mode, and defrag should complete.
Restarting in safe mode:
1. Start Windows, or if it is running, shut Windows down, and then turn off the computer.
2. Restart the computer. The computer begins processing a set of instructions known as the Basic Input/Output System (BIOS). What is displayed depends on the BIOS manufacturer. Some computers display a progress bar that refers to the word BIOS, while others may not display any indication that this process is happening.
3. As soon as the BIOS has finished loading, begin tapping the F8 key on your keyboard. Continue to do so until the Windows Advanced Options menu appears. 4. If you begin tapping the F8 key too soon, some computers display a "keyboard error" message. To resolve this, restart the computer and try again.
Using the arrow keys on the keyboard, scroll to and select the Safe mode menu item, and then press Enter.
However, that doesn't help identify the program that's running. Most often it's a "spyware" program. Let us take a closer look at what is running on your PC. We'll need you to use a free diagnostic tool (HiJackThis) and post a log back here with the results.
Click the HijackThis Guide
in my signature, download it and follow the instructions in the guide.
Most of what it lists will be harmless or even essential, DO NOT delete or modify anything yet! Someone will be along to tell you what steps to take after you post the contents of the scan results.