Intel Core i5 3450 freeze and Gpu artifacts on screen

     Hi guys,

Since when I build my pc 4 months ago ithad sometimes freeze and a sound very weird, then did some testing with memtest86 + for RAM memory, cpu stress tests and all had satisfactory results, no error has occurred. I thought it was the adobe flash the culprit, because every time I crashed when watching videos on youtube, I started using the html5 and freezing constant problem stopped. But still, once in a while itstill fought. What caught my attention is that these crashes to reset the pc, and then he hung up completely and them Power on.

Currently, the problem came back, and this time very randomly, sometimes it happens when I'm playing games (Warcraft, Need for Speed, Skyrim...), watching movies or videos on youtube, it happens 2 things:or the pc hangs and artifacts appearing on the screen,or the pc restarts in the way I described earlier.

I decided to do a more detailed test, because this is really bothering me.

The tests:

-FurMark to stress the GPUs (onboard and offboard)

            Result: In the offboard gpu test was a success without any error, since the onboard video, the pc crashed with less than 1 min test as can be seen in the link below:

http://imageshack.us/a/img204/3143/1000814ef.jpg

           -Memtest86+ for stress test on Memory Ram

            Result: The program spent with my 2 sticks of memory, and then each separately and in different slots, by 6am. No errors were found.

          -Prime 95 to stress the CPU

          Result: no error also.

          I  decided to leave the pc with only 1 stick of memory already onboard video that showed the error very quickly, and to my surprise the pc worked a full day without locking on, redid the test Furmark for 4 hours and monitoring the temperature as the RealTemp. The maximum temperature in one of the colors reached 47 º C only.

This procedure made with the two memories sticks , one at a time, and PC was actually stable.

When I put the 2 sticks of memory in PC (dual Channel), problems reappeared:

http://imageshack.us/a/img843/8767/1000816j.jpg

http://imageshack.us/a/img689/6669/1000815d.jpg

With the offboard GPU these errors happen more also a much smaller scale, with the onboard happen very often.I suspect that might be the processor, but would like the opnion and suggestions to solve the problem.

My configuration:

Intel core i5 3450

Asrock Z77 Extreme 4

8GB gskill sniper 1.25V (http://www.gskill.com/products.php?index=390)

XFX Radeon HD 4850 512 MB

HD SATA-3 500GB seagate barracuda

HD SATA-2 1TB Samsumg

PSU Seasonic 520W 80 plus bronze

Windows 8 Pro

Sorry for the long text and bad english.