Trying to simulate the problem ... I figured out that:
1) When playing a video game, watching a video/movie ... will finally ends with this sequence:
Screen freezes (sound still sounds)
... a few seconds with frozen screen and normal sound ...
... finally: sound crashes and it enter in a infinite mini-loop (random strange sound, depending on the point where the sound player was)
---> it remains like this for hours (unless you reboot/shutdown the computer).
So, trying to isolate the problem (i've done all kind of checks/tests/substituions):
---> The Graphics card is the bad component.
How can I know what kind of issue is? Really I didn't need to perform any graphics test before ... so I don't have any clue on what kind of tools/trips/tricks could be useful to me.
Thank you very much for your info,
PS.1. Curious data: first it started happening after a while playing .... but several days after, it was happening sooner and sooner ... just after a few seconds playing. So I've thought in open my case (cooling-system is a panic on this), and it worked successfully :-) However, after a few days ... it was just not enough, and the problem started again (open or closed case). After checking temperatures I knew it was not a temperature problem ... so this is quite strange !!
PS.2. Tomorrow I'm taking another gpu to remplace it ... but I wanna know how I could know what the problem is,
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