Can't tell if my CPU or motherboard is faulty

Hello, I need help from more experienced people, and I will try to make this as short as possible. Three days ago, I ordered a used GPU. I followed several steps: I uninstalled the old drivers using DDU, removed my old graphics card, and installed the new one. Initially, the new GPU did not work, and I encountered a black screen. I attempted to reseat the GPU multiple times and also reseated the RAM. Additionally, I removed the CMOS battery to reset the BIOS settings. At one point, when I switched my PSU from 0 to 1, I noticed smoke emerging from my motherboard, specifically from the area where all the ports are located, accompanied by a distinct burning smell. I promptly turned off the power to prevent any further damage. After this incident, I checked for visible damage, and while my CPU appeared to be fine from both sides, I did not see any obvious damage on the motherboard either. I carefully reinstalled the CPU and decided to give it another try. My PC managed to power on, but after approximately 30 seconds to one minute of operation, I heard a strange, squeaky screeching sound emanating from my headset, followed by the PC shutting down unexpectedly. Despite this setback, I remained determined and repeated all the previous steps again. After about an hour, I attempted to power on the PC once more, and this time it worked without any apparent issues. I spent hours checking the temperatures and voltages, and everything appeared to be functioning normally. I even played games without any problems. Later, I decided to install my old GPU, so I uninstalled the drivers using DDU once again. However, when I turned off my PC, it did not power on afterward. I tried using three different GPUs, all of which have been confirmed to work in my brother’s PC. I also attempted to use just one RAM stick while reseating it multiple times. Furthermore, I cleared the CMOS and unplugged everything for several hours, hoping this would resolve the issue. I tested my PSU in my brother’s PC, and it worked flawlessly. I even tried using my brother’s PSU in my own PC, but that did not yield any results either. I was able to verify that nearly all components—monitors, cables, GPUs, RAM, and PSU—functioned correctly in my brother’s PC. The only components I could not test were the CPU and motherboard, as I do not have access to another LGA1700 motherboard or CPU. The current behavior of my PC is as follows: when I attempt to power it on, the CPU cooler fan spins, the chassis fans run at full speed, one GPU fan spins while the other appears to have zero RPM, and my keyboard lights up for half a second before turning off again. Each time I press a key, the keyboard lights up for another half second, but the screen remains completely black throughout this process. I suspect that I may have damaged something during the incident when the smoke came out. While I was fortunate enough to get the system running the first time, it has not worked since. I am seeking assistance in determining whether my motherboard or CPU is faulty. My specifications are as follows: CPU: i5-12400F, Motherboard: ASRock H610M-HDV (with the latest BIOS), RAM: 2x16GB 3200MHz (which has been tested in another PC and works), PSU: TUF Gaming 750W (which is one year old and has been tested in another PC, also working), and GPU: RX 6700 XT / RTX 3070 (both of which have been tested in another PC and function correctly).

It is likely your motherboard that is at fault. Typically, a motherboard will sacrifice itself to protect the CPU and other components in the event of a power supply failure or similar incident. Additionally, since you are using a 12th generation Intel CPU, it is insulated from the vminshift self-destruct microcode flaw that affects the 13th and 14th generation Intel CPUs. In general, CPUs are not prone to failure, and it is much more common for a motherboard to fail before a CPU does. This is one reason why older motherboards tend to be more expensive on platforms like eBay, whereas older CPUs are usually more affordable.

This makes sense; thank you for your insight.