More detail about the problem is needed before any advice can be given.
Did the "hard reset" get the monitor working again? I assume it did.
When the monitor turned off, "As if i had turned the monitor off onto standby", that sounds like the power LED on the monitor was flashing on and off, or changed color to indicate it went into its low power sleep mode, is that right? That would also happen if you have the Windows Power Plan set to turn the monitor off after a certain period of time of inactivity on the PC, right? Or if you shutdown the PC and forgot to turn off the monitor.
If the above description fits your situation, then it seems as if there was no signal to the monitor during the gaming sessions. Just like all the other scenarios I mentioned, all of them are no signal to the monitor situations.
The "hard reset" you mentioned I'm guessing was a power cycle of the PC? Meaning you turned the PSU's switch off and on again, or held down the power button on the PC case until it shut off, and then started the PC again? It was after this that the monitor came back to life, correct?
If all of this is correct, then one or a combination of the things listed below could have happened:
The games locked up due to a driver issue.
The video card over-heated due to the stress of gaming and the heat created by the CPU, and crashed the system.
The CPU over-heated due to the stress of gaming and the heat created by the video card, and crashed the system.
The PSU over-heated due to the stress of gaming, and one of more voltages dropped below specification, crashing the system.
AMD FX processors are known to be power hungry, and many AMD boards that were thought to have strong enough voltage regulators (VRMs) for the CPU were found to be lacking in that area. Your CPU has this note associated with it in the CPU support list:
For cooling the CPU and its surrounding components, please install a CPU cooler with a top-down blowing design.
Which really means the VRM heat sinks need air circulation to keep cool. Fortunately, your board has heat sinks on the VRMs, many don't.
What CPU cooler are you using, and how many case fans are you using in your PC case? Any idea what the CPU and GPU temps are while gaming?