More information would help. Off the top if your computer is new or if you have added lots of data the indexing could be running. Make sure defrag isn't running, be sure defender isn't doing a disk scan.
thanks for replying,
the thing is, its almost 80% of the time like that, and no, it was like that since I installed Win8 in October, defrag is off, and how to check if its on and hidden?
If you are using Defender go to the task bar and there should be a little green icon, double click on it and look at the settings and be sure it isn't scanning the drive.
Is the hard drive light running all the time as well?
You could also just click the "Open Resource Monitor" link at the bottom of that window and go to the disk tab to see what process(es) could be causing it.
Can you show us this kind of screenshot of your task manager?
Is your computer suffering performance-wise? I notice that your Read/Write speeds are not at maximum. This might just be Windows having an odd "moment" where the numbers don't make sense.