Dear Kevin,
Thank you for you reply but I had already tried all that.
But a few days ago I found the solution.
I changed the CPU graphics voltage from 1.00 to 1.05. And now the problem is gone. You only need to have a motherboard which let's you do this.
I guess the auto adjusting of the voltage is not working properly.
Hope that people with the same problem will try my solution.
Thanks anyway.
Best regards,
Evangelos