Is your Defrag missing, or just broken?
1. Open 'My Computer,' right-click on a hard drive and go to 'Properties.' Navigate to the 'Tools' tab.
2. Your Defrag is missing and needs reinstalling if: 1) the 'Defragment Now...' button is missing or grayed-out, or 2) when you click on it you get an error message reading, 'The Disk Defragmenter is not installed on your computer'. To install it, double-click the 'Add or Remove Programs' icon in Control Panel, click the 'Install/Uninstall' tab, and then follow the instructions on your screen. Skip to 'Reinstalling Defrag.'

3. Your Defrag is broken and needs repairing if: 1)you are able to open the Defrag program, but nothing happens when you click 'Analyze' or 'Defragment,' or 2)You receive the error message, 'Windows cannot connect to the Disk Defragmenter engine.' Skip to 'Repairing Defrag.'
Reinstalling Defrag
4. In your main hard drive, find the c:\Windows\Inf directory. If your system directory is not on your c: drive or not named Windows, find it by clicking on 'Start,' then 'Run' and typing %Windir%\Inf in the box.
5. Find the file named dfrg.inf.
6. Right click the file and select 'Install.'
Repairing Defrag
7. Click 'Start,' then 'Run,' and run this command: regsvr32 dfrgsnap.dll
8. Click 'Start,' then 'Run,' and run this command: regsvr32 dfrgui.dll
9. Run Defrag.