Aris Adamantiadis 
💲PaidI made some quick tests with ComfyUI on my computer and RTX4090. For some reason, there's one type of workload that consistently shutdowns the computer (black screen, everything stops except for the power led.) I have to switch it off for 1 min then it boots again. I suspected the 850w PSU may be a bit dated, but the behavior continues consistently when I change max gpu power to 200w, disable cpu boost, reduced gpu and memory speed etc. I'm lost, I'm not 100% sure it's on the PSU despite it being a good replacement candidate.
Skate Cloud@aris try reseating the RAM and GPU if you can. RAM first preferably and while you have the RAM out, try cleaning it with a soft dry cloth and blowing on the contact pins to ensure they are clean. Might just be some very slight dust in the contact pins of one of the RAM sticks (if you have multiple)
@skatecloud would it cause a hard crash? I have 4x16G, it's worth trying anyway. Good idea trying to move the PCIe slot because I'm sure PCIe errors can hard reset the computer.
@aris I have had “dirty” RAM cause a few hard crashes. System works fine until you need to use the actual capacity in that stick and thats when issues occur(system freeze or a sudden shut down). Dirty RAM in general can just acts funky. Sometimes it prevents booting up entirely other times it can take hours to actually cause a problem.
@skatecloud I'll do a memtest86 in the meantime.
@skatecloud passed with 0 errors... I'll check the PCIe slot again.
@aris any luck?
@skatecloud I haven't had time to swap the gpu but the memtest is negative. I received the new 1kW PSU, I'll install it this week.
@skatecloud I installed the new PSU, it works! I blame the shitty 4x PCIe to nVidia cable setup I had on the previous PSU.
@aris hope the gpu behaves now. That 12vhpwr socket can be a bit troublesome