Please help, I've recently built my very first custom pc and it's suddenly slow after installing steam and a few games.

So I've recently had a custom desktop pc built because I've finally gathered enough money to make a pc of choice. I didn't have much insight or the help from any of my friends. So I've decided to make one from my own research and my personal knowledge. Here are my specs:

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System Information
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Time of this report: 10/16/2016, 22:53:54
Machine name: RENORIGIN
Machine Id: {DD6CF405-87B8-4636-ADAF-ADAE9D1EBC19}
Operating System: Windows 10 Pro 64-bit (10.0, Build 14393) (14393.rs1_release_inmarket.161004-2338)
Language: English (Regional Setting: English)
System Manufacturer: To Be Filled By O.E.M.
System Model: To Be Filled By O.E.M.
BIOS: P3.60
Processor: Intel(R) Core(TM) i7-6800K CPU @ 3.40GHz (12 CPUs), ~3.4GHz
Memory: 8192MB RAM
Available OS Memory: 8112MB RAM
Page File: 2867MB used, 12884MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 12
DX Setup Parameters: Not found
User DPI Setting: Using System DPI
System DPI Setting: 96 DPI (100 percent)
DWM DPI Scaling: Disabled
Miracast: Available, with HDCP
Microsoft Graphics Hybrid: Not Supported
DxDiag Version: 10.00.14393.0000 64bit Unicode
DxDiag Previously: Crashed in DirectInput (stage 1). Re-running DxDiag with "dontskip" command line parameter or choosing not to bypass information gathering when prompted might result in DxDiag successfully obtaining this information

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DxDiag Notes
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Display Tab 1: No problems found.
Sound Tab 1: No problems found.
Sound Tab 2: No problems found.
Sound Tab 3: No problems found.
Input Tab:

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DirectX Debug Levels
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Direct3D: 0/4 (retail)
DirectDraw: 0/4 (retail)
DirectInput: 0/5 (retail)
DirectMusic: 0/5 (retail)
DirectPlay: 0/9 (retail)
DirectSound: 0/5 (retail)
DirectShow: 0/6 (retail)

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Display Devices
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Card name: NVIDIA GeForce GTX 1080
Manufacturer: NVIDIA
Chip type: GeForce GTX 1080
DAC type: Integrated RAMDAC
Device Type: Full Device
Device Key: Enum\PCI\VEN_10DE&DEV_1B80&SUBSYS_85911043&REV_A1
Device Status: 0180200A [DN_DRIVER_LOADED|DN_STARTED|DN_DISABLEABLE|DN_NT_ENUMERATOR|DN_NT_DRIVER]
Device Problem Code: No Problem
Driver Problem Code: Unknown
Display Memory: 12200 MB
Dedicated Memory: 8144 MB
Shared Memory: 4056 MB
Current Mode: 1920 x 1080 (32 bit) (60Hz)
Monitor Name: Generic PnP Monitor
Monitor Model: LG IPS FULLHD
Monitor Id: GSM5AB7
Native Mode: 1920 x 1080(p) (60.000Hz)
Output Type: DVI
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So the pc was really really fast at the beginning and everything was working perfectly fine. I was playing Skyforge and that's all i had for about a week. After that I've decided to download my steam games and here comes the problem. After installing a couple of the games my pc started to slow down drastically and I was wondering why? Since it wasn't even using a whole lot of space comparing to what I have in reserve. I've been checking throughout task manage and everything is always low. As in Memory is always 30% or under, CPU is always 5% or under, Disk is always 5% or under and I was struggling to find out what the problem was. I've been browsing on forums for weeks trying to fix this on my own. I've tried using DDU and reinstalling the news driver for my graphics card, and now that I'm desperate I don't really know what to do. Please help