HDD stuck at 50%

[TC6]

So I tried pretty much every single method that was given to me on Google and they didn't work at all. My Hard Drive always caps at 50% when I have my SSD plugged in using another SATA cable. I'm extremely confused why it happens because I've never seen this happen before. If I unplug the SSD then it works fine without issues.

Extra info:
- My HDD is my system drive 
- SanDisk SSD PLUS 240 GB Sata III 2.5 Inch Internal SSD, Up to 530 MB/s, Black
- The SSD works without issues when I transfer files it just takes away 50% of my HDD when I check Task manager. As seen below in the screenshot

* Edit: I have tried switching the SATA cables and even buying new ones and it didn't work, it still stuck at 50%. 
 

[rcmaehl]

Disk shows activity for ALL DISKS, not just C:. What does the Performance Tab drive graphs show?

[TC6]

3 hours ago, rcmaehl said:

Disk shows activity for ALL DISKS, not just C:. What does the Performance Tab drive graphs show?

I just now realized... It might not even be stuck at 50%. I think I was looking at the incorrect area because I can see it use 100% of the HDD now. I think I was just being stupid. Oops thanks for mentioning that.