a little update on this.
i've run everest to check on temperatures and after shutdown, i turn it on immediately but no message appeared, what i did saw was CPU temperatures going around 77-70 ºC, not sure if that is normal or something.
i think i've already mentioned i believe it only shuts down when im doing heavy load task or heavy multi tasking.
on the beeping sound, i looked it up and i cant seem to find a stable "analysis" they appear randomly and sometimes they are totally different
edit.
used also speedfan to test temps. now im 99% sure its CPU overheating, tested under some load, reached 80 to 90ºC