I installed Windows 7 Ultimate and it worked well. But I realized that I needed Windows 7 Professional. I installed the new edition. Then I tried to defragment my HDD (I use Ashampoo Winoptimizer 7), but I couldn't see my D: partition. Windows Disk Management recognized that drive D: has 100% free space. In Explorer I see the files on it and I can use it like my other partitions.
Why can't Windows Disk Management see that my D: drive isn't just free space?