You have a bad cable, or you NEED a new harddrive. This is critical as the stats I see and the problem your describing is hard drive failure. The reason when your doing nothing its aactive time is 0 is because its doing nothing.
When you start a download or game, it has to re-read that same information on your damaged drive several times, this is where the disk que comes in, so every task after that one is now in a disk que.
I would highly reccomend a hybrid drive and use a regular for storage. To be quite honest, I would never get a physical hard disk drive in this age anymore, to much room for failure. especially when your most valuable and critical information about your life is stored on something so fragile.
REPLACE YOUR DRIVE, Use a backup program to save your files. I would NOT use this drive any more, the more reads/writes is the more you are destroying the drive.
for those who wonder,
The reason why when you buy a 1tb drive and its only like 970gb or 256gb drive and its 240gb is the extra space you cannot see is left from the factory, this space is allocated for bad sectors. when the drive startts going bad if the disk cant write or read a sector it will mark it as bad, which then allocates it to this extra space, so it is never used again, this space will fill up and once it maxes out, then thats when you see the issue you are having, because its being forced to use bad sectors.