If you are sure there is no virus on your Windows computer, no your application is running in the background, like Antivirus on the scanning process, etc. and you still see the hard drive indicator is always busy. or from the task manager the disk activity get the high value 90% or more. whats is the cause?.
One possible cause is : the computer is optimizing your hard drive, defragmenting the drive. This is happen because at default Windows 10 has optimization schedule automatically which it is set one time a week.
You can set/change the optimization schedule, or you can stop/turn off it (manual defragment process).
To set the Optimization Schedule :
1. Open File explorer.
2. Right click at Local Disk, then choose Properties.
3. Choose Tools tab.
4. Click Optimize button.
5. At Optimize Drives window click Change setting button. Then you can change the schedule or even turn off it.