My Vista Ultimate defrag function does not work. Clicking on defrag to start it's function seems to begin the process, but the icon never stops rotating, nor is there an indication that the disk has finished it's defrag. I have tried this a dozen times, with the longest run period being just over four days. My computer has a 320 GB hard drive, and is a Dell laptop. I have tried to run defrag.exe at the command prompt, but get a message that it can only be run by the administrator. I have not tried a clean boot, as I cannot understand it. My only virus software is Microsoft Essentials. Where do I go from here?