Hello, before defragmenting disk, you should do something in advance.
1. You should clean up the junk files and information.
Since your system work for a long time, the junk files may cram many unconscious operations may result in junk files. They are temporary files when installing the programs, cache files after browsing, DLL files left by deleting software and error files produced by shutting down the computer forcedly.
It is common that most users are inclined to use the disk cleaning up programs in the Windows, at the same time, you can also turn to certain more powerful defragmenter to help you.
2. You should check and restore any mistake in the hard disk.
Of course, you can have a try of the Disk Scan Program of Windows firstly. Although it really takes a lot of time to repair it, as long as you are patient enough, the most errors and mistakes can be restored after complete and detailed scanning.
And more to
http://ezinearticles.com/?Disk-Defragment---Why-I-Cannot-Continue-to-Defragment-Disk&id=3165935