3 days ago I upgraded to Windows 8 Pro. I upgraded my CPU, RAMS and HDD. I made clean install on new HDD.

It's 3rd time my system shutdown without any reason. For a first time, I was watching TV next to my PC and then noticed that PC is off. After few hours, I've been playing a game and system shutdown again. Without any warning, error - just turned off, like it would when pressing power button for a few seconds.

I went to bios and checked settings. I turned off CPU Cool 'n Quite, because I tought it's causing this problem. Everything worked fine for next few hours. Now, my PC shutdown again, while I was playing a game. I immediately turned on PC and went in bios. CPU temperature was 50*C and motherboard 37*C, so I think it's not overheating (I cleaned my whole PC 3 days ago). 

I also think it's not PSU, because it worked fine with Windows 7. 

There was a bunch of logs after I turned on PC.

Event Logs:

Log 1:

Log Name: System
Source:  EventLog
Date: 11.7.2013 12:50:24
Event ID: 6008
Task Category: None
Level:Error

Description:
The previous system shutdown at 12:43:45 on 11.7.2013 was unexpected.

Log 2: 

Log Name: System
Source: Microsoft-Windows-Kernel-General
Date: 11.7.2013 12:50:17
Event ID: 6
Level: Error

Description:
An I/O operation initiated by the Registry failed unrecoverably.The Registry could not flush hive (file): ''.

Log 3:

Log Name: System
Source: Microsoft-Windows-Kernel-Power
Date: 11.7.2013 12:50:18
Event ID: 41
Task Category: (63)
Level: Critical

Description:
The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.

Log 4:

Log Name: System
Source: Microsoft-Windows-Kernel-PnP
Date: 11.7.2013 12:50:18
Event ID: 219
Task Category: (212)
Level: Warning

Description:
The driver \Driver\WudfRd failed to load for the device ROOT\WPD\0000.

Log 5:

Log Name: Security
Source: Microsoft-Windows-Eventlog
Date: 11.7.2013 12:50:25
Event ID: 1101
Task Category: Event processing
Level: Error

Description:
Audit events have been dropped by the transport.  0

Log 6:

Log Name: System
Source: AFD
Date: 11.7.2013 12:50:22
Event ID: 16001
Task Category: None
Level: Warning

Description:
The description for Event ID 16001 from source AFD cannot be found. Either the component that raises this event is not installed on your local computer or the installation is corrupted. You can install or repair the component on the local computer.

If the event originated on another computer, the display information had to be saved with the event.

The following information was included with the event: 

\Device\Afd
\Driver\aswTdi

PC Specifications

PSU: 600W, bought it 3 months ago

CPU: AMD FX 6300 3.5 Ghz (6 - core CPU)

GPU: HD 7770 (1GB)

RAM: 2x4GB DDR3 1600

HDD: WD Blue 1 TB

Does anyone know how to solve problem with system shutdown without any reason??? 

Why I always read about pc problems when these guys use AMD processors?

Nevermind, that's just a detail.

Are you still checking the processor temperature via the BIOS? Because there are programs where you can check each core about the temperature while being in Windows and not BIOS.

What you could also do, opening up your computer and leave it open than let the computer be on for a long time and check if it will shutdown again. When it will not, it's most likely a temperature issue.

My friend had that problem with his graphicscard. As soon as he opened the computer, he had no more problems anymore (though you should not then leave it open, you should search for a fix for that).

As I linked before: http://www.techpowerup.com/realtemp/

Monitor your temps while you're actually using your computer, not just bios. As it stands it appears you are just shooting in the dark.

As someone else stated you can also remove the side cover from your computer case to increase ventilation. While you're at it, observe whether the heat sink fan is actually running freely.

I have side cover opened all the time and that's why I doubt its overheating... My PSU is blowing out almost cold air. 

I just came home from a shop and changed thermal paste. I don't really think that will stop shutdown, but let's try.

RealTemp does not work for my CPU. At installation it says : AMD FX 6300 is not supported.

Try this temp monitor: http://www.alcpu.com/CoreTemp/

It claims to support your processor.

I downloaded CoreTemp and it says temp of each CPU core is 22*C... And ASrock Utility says CPU temp is 40*C, just like BIOS... So I guess CoreTemp is giving out wrong temp.

I installed CPUID HW Monitor and it show temp. of three cores only -> 21*C, 21*C and 30*C

 

How to  get my account verfied? I'd like to give a link but can't.

Perform temp readings under load if you haven't already. I also read back and saw that there was a question about your ram settings. Consult the ram manufacturer and the docs for your mobo. You might also want to perform a ram test. Memtest is a good utility: http://www.memtest86.com/

Almost all of Event Log errors disappeared after uninstalling Avast... Maybe that was causing my PC to shutdown. I googled a bit and read avast forum. Many people said Avast is causing many errors, PC crashes, random restarts, shutdowns. I really hope it was Avast causing my problems.

I installed Windows 8.1 Preview to my PC a week ago and it worked good. When I installed Avast, PC went crazy. I was not able to uninstall it nor run system restore, system was spamming me with errors - every 3 seconds one error. I had to reinstall Windows. 

So Avast strikes again. In retrospect it might have helped to post .dmp files for analysis but the symptoms sure sounded like a thermal problem. FWIW the av I'd recommend is ESET Nod32: http://www.eset.com/us/search-brand-eav/?CMP=KNC-g-ag&mkwid=st7qyBI5G&pcrid=21197746690&pmt=e&pkw=eset%20nod32&gclid=CJSd55L0qrgCFTDZQgodCXoAdA

It's not free but in my opinion beats most everything out there in terms of protection and has a small system footprint. Whatever you do I'd recommend you stay away from anything Norton.

In the event that your problem recurs, post your system's memory.dmp file to your skydrive in a shared public folder. Post the link here and someone will take a look at it.

http://www.hardcore-games.tk/wp/hw/tim.php

http://www.hardcore-games.tk/wp/vc-overheating.php

Dump files does not exist on my PC. 

I tried everything and can't find it. In the end I downloaded WhoCrashed and that is what WhoCrashed says:

"Crash dump directory: C:\Windows\Minidump

Crash dumps are enabled on your computer.

No valid crash dumps have been found on your computer"

I bought Thermal Paste with Thermal Conductivity < 1.46W/mK