repro : Format > Install Win 7 > Install Drivers > Windows Update > Install CK2 > Patch
And If I play the game...nothing happens and everything is okay.
But If I press alt+tab (first time) during the gameplay and rejoin the game, since then, If I use mouse scrolling, very soon screen freezes...but at that point, If I press alt+tab and rejoin game, I can play again, and so scroll again with the keyboard. (Instead of keyboard scrolling, If I use mouse scrolling again, very soon It freezes again...of course I can solve that problem by press alt+tab and rejoin the game again and again

)
So actually It's not 'freeze' of whole computer...but It seems that some kind of alt+tab related graphic problem.
This might seem little weird.
But I tried many things and finally discovered that consistency.
cf. Beyond this problem, keyboard scrolling is very smooth but mouse scrolling is very laggy...
Thank you and attaching my dxdiag.txt.
------------------
System Information
------------------
Time of this report: 8/31/2012, 20:09:26
Machine name: SU79EU7K-PC
Operating System: Windows 7 Ultimate K 64-bit (6.1, Build 7601) Service Pack 1 (7601.win7sp1_gdr.120503-2030)
Language: Korean (Regional Setting: Korean)
System Manufacturer: LENOVO
System Model: IdeaPad Y460
BIOS: Rev 1.0
Processor: Intel(R) Core(TM) i5 CPU M 430 @ 2.27GHz (4 CPUs), ~2.3GHz
Memory: 6144MB RAM
Available OS Memory: 5940MB RAM
Page File: 2412MB used, 9466MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 11
DX Setup Parameters: Not found
User DPI Setting: Using System DPI
System DPI Setting: 96 DPI (100 percent)
DWM DPI Scaling: Disabled
DxDiag Version: 6.01.7601.17514 32bit Unicode
------------
DxDiag Notes
------------
Display Tab 1: No problems found.
Sound Tab 1: No problems found.
Sound Tab 2: No problems found.
Input Tab: No problems found.
--------------------
DirectX Debug Levels
--------------------
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)
---------------
Display Devices
---------------
Card name: ATI Mobility Radeon HD 5650
Manufacturer: ATI Technologies Inc.
Chip type: ATI display adapter (0x68C1)
DAC type: Internal DAC(400MHz)
Device Key: Enum\PCI\VEN_1002&DEV_68C1&SUBSYS_395117AA&REV_00
Display Memory: 3694 MB
Dedicated Memory: 980 MB
Shared Memory: 2714 MB
Current Mode: 1366 x 768 (32 bit) (60Hz)
Monitor Name: General PnP Monitor
Monitor Model: unknown
Monitor Id: SEC3049
Native Mode: 1366 x 768(p) (60.001Hz)
Output Type: Internal
Driver Name: atiu9p64.dll,atiuxp64.dll,atiuxp64.dll,atiu9pag,atiuxpag,atiuxpag,atiumdva,atiumd6a.cap,atitmm64.dll
Driver File Version: 8.14.0001.6143 (English)
Driver Version: 8.772.0.0
DDI Version: 11
Driver Model: WDDM 1.1
Driver Attributes: Final Retail
Driver Date/Size: 8/31/2010 20:16:26, 37376 bytes
WHQL Logo'd: Yes
WHQL Date Stamp:
Device Identifier: {D7B71EE2-2B81-11CF-E563-5019A1C2C535}
Vendor ID: 0x1002
Device ID: 0x68C1
SubSys ID: 0x395117AA
Revision ID: 0x0000
Driver Strong Name: oem6.inf:ATI.Mfg.NTamd64.6.1:ati2mtag_Manhattan_PXAI:8.772.0.0

ci\ven_1002&dev_68c1&subsys_395117aa
Rank Of Driver: 00E60001
Video Accel: ModeMPEG2_A ModeMPEG2_C
Deinterlace Caps: {6E8329FF-B642-418B-BCF0-BCB6591E255F}: Format(In/Out)=(YUY2,YUY2) Frames(Prev/Fwd/Back)=(0,0,1) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_PixelAdaptive
{335AA36E-7884-43A4-9C91-7F87FAF3E37E}: Format(In/Out)=(YUY2,YUY2) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_BOBVerticalStretch
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(YUY2,YUY2) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY
{6E8329FF-B642-418B-BCF0-BCB6591E255F}: Format(In/Out)=(UYVY,UYVY) Frames(Prev/Fwd/Back)=(0,0,1) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_PixelAdaptive
{335AA36E-7884-43A4-9C91-7F87FAF3E37E}: Format(In/Out)=(UYVY,UYVY) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_BOBVerticalStretch
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(UYVY,UYVY) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(YV12,0x32315659) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{3C5323C1-6FB7-44F5-9081-056BF2EE449D}: Format(In/Out)=(NV12,0x3231564e) Frames(Prev/Fwd/Back)=(0,0,2) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_PixelAdaptive
{552C0DAD-CCBC-420B-83C8-74943CF9F1A6}: Format(In/Out)=(NV12,0x3231564e) Frames(Prev/Fwd/Back)=(0,0,2) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_PixelAdaptive
{6E8329FF-B642-418B-BCF0-BCB6591E255F}: Format(In/Out)=(NV12,0x3231564e) Frames(Prev/Fwd/Back)=(0,0,1) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_PixelAdaptive
{335AA36E-7884-43A4-9C91-7F87FAF3E37E}: Format(In/Out)=(NV12,0x3231564e) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY DeinterlaceTech_BOBVerticalStretch
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(NV12,0x3231564e) Frames(Prev/Fwd/Back)=(0,0,0) Caps=VideoProcess_YUV2RGB VideoProcess_StretchX VideoProcess_StretchY
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(IMC1,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(IMC2,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(IMC3,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(IMC4,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(S340,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
{5A54A0C9-C7EC-4BD9-8EDE-F3C75DC4393B}: Format(In/Out)=(S342,UNKNOWN) Frames(Prev/Fwd/Back)=(0,0,0) Caps=
D3D9 Overlay: Not Supported
DXVA-HD: Not Supported
DDraw Status: Enabled
D3D Status: Enabled
AGP Status: Enabled