Any computer nerds here? Hard reboots

[rado84]

So I bought a premade system last year.

AMD A8-6600K APU
8 Gigs DDR 3
Win 7 64

The only thing I did was to deactivate the built in videocard and to replace it with a Geforce GTX 650 ti.

These last few weeks I have hard system reboots when either watching web videos, such as Youtube or Vimeo and in games like Mass Effect 3 where there are cinematics. It only happens when videos are playing. Not during actual gameplay and not when the computer is simply running other programs.

I browsed the web extensively for an explanation and installed Speedfan to do some monitoring. Now I noticed that CPU temperature as well as Core temperature go wild when a video is played. From an idle of 42 degrees C (CPU) and 7 degrees C (Core), temperature rises to 70 CPU and 59 Core within three minutes. So, my guess is, at longer videos it performs an emergency shutdown because temperatures actually go to high.

GPU temperature on the other hand stays constant.

That's inexplainable to me, since simply playing a video shouldn't stress the CPU as much.

That's why I never buy premade systems and always build the system myself - component by component. Thus I always know exactly what is in my computer and its quality.
AMD CPUs have always been and will probably always be stoves.
As for the high temps, they shouldn't bother you much. A video can raise the CPU temperature (GPU temp as well) depending on the codec used for the video conversion. x264 and x265 raise my CPU and GPU temps a little while a regular XviD doesn't change the temps at all. The best you can do is to put some silver thermal paste on your GPU and CPU and manually control the fan speed of GPU. As for the CPU, you can enter BIOS and set speed for the CPU fan but that depends on your motherboard and the BIOS version it has and whether or not your CPU fan has 4 pins or 3. If it has 4 pins attached to the motherboard, you could set speeds for it but if it's with 3, you can't.