I have had this problem over quite a while now, thorough multiple Linux kernel versions and distributions, as well as replacement of all components, aside from my main HDD - RAM, GPU(twice), mother board, CPU, power supply. What happens is, at one point during the operation of the PC, it will hardlock - everything stops working, external HDD is not shut down correctly and continues to spin until I plug it out and in, there are no system/kernel logs of any kind, and no otherwise nothing that would suggest a cause. Another reason for my suspicion is that the failures happen almost exclusively during HDD read/write activity - shutdown(happens nearly 1/3 of the time so far, it's only been few days though), launching programs, and once during operation of apt. I hope the post is descriptive enough, if you need any additional info, ask(and tell me how to prepare/obtain it), and I will provide. If I'm wrong, point me in the right direction. Thanks in advance.