Solution is to run disk defragmentation program.
Run Disk Defragmentation in Windows
1. Double click on “My Computer” icon on your desktop
2. Right click on hard disk you want to defragment and click on “Properties”
3. In “Local disk properties” dialog, click on “Tools” tab
4. Click “Defragment now…” button
5. In “Disk Defragmenter” program click “Defragment” button
Disk defragmentation can take few hours. Make sure that you have at least 15% free space before defragmenting. Best thing to do is to close all programs, and run defragmentation at night without using your computer.