Extreme DWM/Aero Lag even with Good PC and Strong GPU

Hi. Recently I got a new computer from second hand shop (DELL OptiPlex 990 MT) and upgrade everything with this specs:

- i5-2400
- 8GB DDR3 RAM
- 500GB HDD
- 550w PSU
- NVIDIA GTX 1060 6 GB
- LG 4K IPS Monitor
- Windows 7 Professional OEM Service Pack 1 64 Bit

My problem started 1 hour ago today and I don't know why. While Browsing the Internet on Google Chrome. I'm playing Facebook for about 10 minutes. Later, It's starting to Lag and Laggier. Makes me angry and Sometimes there is micro-freezes as well. Also YouTube 60 FPS Videos make a heavy lag and unwatchable. I played HTML5 Games like Cut the rope. It's lagging and my Game Damned me that My Computer is slow. Also PC or Steam Games run at 60 FPS Constant at Medium Settings. That shouldn't be a problem as well. I don't know if it is a 4K monitor issue. I'm running 4K native resolution (3840x2160). If I turned the resolution down to 1920x1080 and can't remember that still having lag. But the lag does often. Related to CPU Bottlenecking? I'm using Anti-Virus is Kaspersky Total Security.

Has anyone figured this out?

This is a Same Duplicate Thread:

AERO themes causes severe lag in the web browsers.

Dwm.exe (Aero/Desktop Composition) lag - has anyone figured this out?

Lag/Laggy animations with multiple displays (Extend desktop)

DWM.exe stuck at 10-12% cpu, causing stuttering

From your post it is not clear that dwm.exe is producing these symptoms. If so, do the symptoms disappear if you disable it? They should, if dwm is the problem.

Have you tried the fix that worked for the guy in your second link? He says adding the following keys to regedit fixes it.

--------------------------------------
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\DWM]

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\DWM\Schedule]
"FrameRateMin"=dword:0000003c

[HKEY_CURRENT_USER\Software\Microsoft\Avalon.Graphics]
"Force10Level9"=dword:00000001

For FrameRateMin...

0000003c = 60, if you run your monitors are 60hz.
00000078 = 120, if you run at 120hz.
00000090 = 144, if you run at 144hz.

Open Windows update and do a manual search for updates. Does it run forever?

Change your theme to a classic (without aero). Does it fix the problem?

Is your graphics card driver up to date?