You have a beefy enough power supply and the rest of the components look good, too. BUT, there's one exception that i can see. Your motherboard has four RAM memory slots, and RAM usually comes in 2GB, 4GB, or 8GB increments. So, how is it that you have 28GB of RAM? If 28GB is not a typing error then you have have an assymetric / uneven memory setup with something like 3x8GB + 1x4GB sticks of RAM. An even 2x8GB or 4x8GB would surely be better.
I suggest that you remove all but one stick of RAM. Test the computer with 1x8GB and see what happens. (In fact, test each and every stick one at a time to see if a faulty or substandard stick is causing the problem). Then try 2x8GB and test again. If that resolves the slow performance then either settle on 2x8GB or get another identical 2x8GB kit to make it 32GB total. As i'm sure you know there's very little benefit from 32GB of RAM over 16GB unless you're doing some heavy multi-tasking or video editing.
If RAM testing doesn't fix / resolve the slow performance, you might try running a simple version of Linux by booting from a CD or a USB flashdrive. Puppy Linux or Puppy Slacker are free to download and, once they boot up from the CD or flashdrive they will then run entirely in RAM memory if i'm not mistaken. You can download, burn to disc and boot up all in the space of about 10 minutes, so it should be fairly easy to test the computer with a different operating system. If performance is quick then you should definitely consider doing a fresh install of Windows from scratch after reformatting the hard drive (you do have an SSD, right?).
im rather new to pc building and my experience has been pretty trial and error, but I've ran into a problem i dont know how to fix. my specs are:
AMD FX 6300 cpu
28 GB DDR3 ram
64-bit windows 10
MSI GeForce GTX 960 4GB DDR5
MSI 970 gaming motherboard
725w power supply
i recently upgraded my motherboard to the 970 from a gigabyte am3+ 1333 760g micro because i thought that it was bottlenecking my pc, but after installing the new motherboard and installing the drivers, i ran into incredibly slow bootups, app startups, game crashes and even my google chrome crashing as well. after running some updates to some of the drivers, the chrome crashes have stopped but my pc still runs very slow to what it used to. Any suggestions?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic