Games start lagging in 4-5 minutes after I started them

Every game starts to lag in 4-5 minutes after I start the game. This is started almost a week ago, I tried to find a solution online but none have helped me so far so I finally decided to post my problem here. Now by every game, I mean almost each and every game lags after few minutes(except for CS 1.6, don't know why). Even the games that I run on Bluestacks (Governor of Poker, FIFA mobile, etc.) or on Windows store (Asphalt Extreme or Asphalt 8) start to lag(this is the limit, its unbelievable!). I am sure that there is no issue with the temperatures of GPU and CPU, I have been using this PC since almost 3 years. I don't know if there's a layer of dirt in between cooler and the CPU but other than that I have done almost everything I can. I have checked that the temps are ok, PSU is proper(been using it since 3 yrs), RAM is good enough(8GB). I have provided proper specs of my rig below right from DxDiag:

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System Information
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Time of this report: 6/29/2017, 01:21:16
Machine name: UK
Machine Id: {A602359A-FFCA-4C1A-9B68-AD4401449D1F}
Operating System: Windows 10 Pro 64-bit (10.0, Build 15063) (15063.rs2_release.170317-1834)
Language: English (Regional Setting: English)
System Manufacturer: Gigabyte Technology Co., Ltd.
System Model: To be filled by O.E.M.
BIOS: BIOS Date: 09/19/12 18:11:30 Ver: 04.06.05
Processor: Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz (8 CPUs), ~3.9GHz
Memory: 8192MB RAM
Available OS Memory: 8154MB RAM
Page File: 7368MB used, 2704MB 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: Not Available
Microsoft Graphics Hybrid: Not Supported
DxDiag Version: 10.00.15063.0000 64bit Unicode

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Display Devices
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Card name: NVIDIA GeForce GTX 760
Manufacturer: NVIDIA
Chip type: GeForce GTX 760
DAC type: Integrated RAMDAC
Device Type: Full Device
Device Key: Enum\PCI\VEN_10DE&DEV_1187&SUBSYS_426519DA&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: 8140 MB
Dedicated Memory: 4063 MB
Shared Memory: 4076 MB
Current Mode: 1920 x 1080 (32 bit) (60Hz)
Monitor Name: Generic PnP Monitor
Monitor Model: 23EA53
Monitor Id: GSM59A9
Native Mode: 1920 x 1080(p) (60.000Hz)
Output Type: HDMI
Driver Name: C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_2d81f3535ced17c6\nvldumdx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_2d81f3535ced17c6\nvldumdx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_2d81f3535ced17c6\nvldumdx.dll,C:\WINDOWS\System32\DriverStore\FileRepository\nv_dispi.inf_amd64_2d81f3535ced17c6\nvldumdx.dll
Driver File Version: 22.21.0013.8253 (English)
Driver Version: 22.21.13.8253
DDI Version: 12
Feature Levels: 11_0,10_1,10_0,9_3,9_2,9_1
Driver Model: WDDM 2.2
Graphics Preemption: DMA
Compute Preemption: DMA
Miracast: Not Supported
Hybrid Graphics GPU: Not Supported
Power P-states: Not Supported
Driver Attributes: Final Retail
Driver Date/Size: 07-06-2017 05:30:00 AM, 885216 bytes
WHQL Logo'd: Yes
WHQL Date Stamp: Unknown
Device Identifier: {D7B71E3E-52C7-11CF-575A-68621BC2DB35}
Vendor ID: 0x10DE
Device ID: 0x1187
SubSys ID: 0x426519DA
Revision ID: 0x00A1
Driver Strong Name: oem5.inf:0f066de34a988f8e:Section018:22.21.13.8253ci\ven_10de&dev_1187
Rank Of Driver: 00D12001
D3D9 Overlay: Supported
DXVA-HD: Supported
DDraw Status: Enabled
D3D Status: Enabled
AGP Status: Enabled
MPO Caps: Not Supported
MPO Stretch: Not Supported
MPO Media Hints: Not Supported
MPO Formats: Not Supported

I hope above mentioned System Information and Display Devices will suffice, would like to know what's causing this problem and is it solvable or not without purchasing anything

UPDATE: SOLVED the problem

I cleaned the dirt between CPU and its cooler, seems as if the solution I kept as the last resort was my solution after all.