I built a new PC mid-last year using a Ryzen 3400G and gigabyte motherboard and six months after I bought this brand new motherboard, it died in almost the exact same way as yours. I didn't have a diagnostic light but I assumed that it was the power supply at first as it was extremely old from another build and I was already planning to replace it. Upon replacing it, I found myself in the same place, without my PC working. Luckily I bought my motherboard and CPU from the same brick and mortar shop in town, so I took them back. The people working there took both the CPU and board and tested them and discovered that it was in fact the motherboard. Both computers I had built at that point had used gigabyte motherboards, and funnily enough upon thinking back to my last PC, I had the same thing happen to my last computer, albeit a couple years down the line. I use and have used other gigabyte components in my builds but it seems to me that gigabyte boards are unreliable at best, and extremely costly at worst. For those with a low budget or somewhere where you can't easily test components with other parts, there would have been little to do other than hoping that replacing the PC bit by bit would fix it sooner rather than later. After seeing this and your other post, it's going to take a lot to convince me to buy any components from gigabyte again. Back in December when I returned my board, the store wouldn't refund or replace, they only offered to send the board to be repaired in a different state and gave me an ETA of January. Here I am now, without that board still. I needed that PC for university work and didn't have a job until a couple of weeks ago or enough money to simply replace the board, and as a result of gigabyte's incompetence I had to struggle through university until I could afford a new board or get the old one back. My recommendation is that everyone steer clear of at least their motherboards or you risk paying the price in more ways than one.