@Sylver:
Well, those values are enough to stress the graphics...
Anyway, how have you been these days?
Best regards
The board didn't shut down anymore. Well, to be more precise, it didn't do what I told you about. I tried the PC at a friend's place with a 19-inch widescreen monitor for several hours and nothing happened, but only for a little while in Metro 2033, then in Dirt 3 and Alan Wake for a while, all at a resolution of 1360x768, which is low compared to those who play with large monitors. Then, after several hours playing PES, I saw that nothing happened. That game is very light.
As I was told, it was either the power supply that was insufficient, something wrong with the board, or even the temperature. If it was something like that, it only happened in a heavy game like Metro 2033. After those two times it shut down, it didn't happen again, but I was left with the doubt about the video card doing that. It's all a mystery.
Today, with a little more heat, the card reached a maximum of 60 degrees and the fan is louder. Reading on Google, many people say that XFX cards are hotter and that other manufacturers like Sapphire or MSI are better. Well, I already bought the XFX and it's the one I have now, and I can't complain. It performs well except for what happened. I have no complaints. I play everything at maximum with my monitor, obviously.
To be honest, when it happened, it was sudden. I didn't notice the game freezing or slowing down. It was running well, which is why it surprised me what happened.
Today I tried Resident Evil Operation Raccoon City for a while at 1280x1024 with everything at maximum on my 17-inch monitor and nothing happened. It moves really well. Obviously, I know I play at low resolutions and my monitor is very small, but that game must demand something from the HD 7770. But I don't know if as much as Metro 2033.
I did see that Resident Evil says a HD 6950 is recommended, which is much bigger than my card, but it's probably for playing at higher resolutions.
If there's something wrong with the card, I didn't notice it anymore because it didn't restart. But if something happens, I'll post about it.
It could also be something else, I don't know. Maybe a fault in the motherboard or the power supply that caused that. But it's very difficult to know and in this world of PCs there are many mysteries 
Thank you very much for all your opinions. I know that from the advice of people who know more, you can always learn something.