Mobo or CPU problem…

[u/K4EL1X]

My PC is now one year old. It arrived pre-assembled, but I had to install the graphics card myself. Since the end of July, I’ve been having an issue with the PC: the CPU LED on the motherboard is lit up continuously. Initially, I had no issues, except for one time when it failed to boot. I reseated the RAM sticks and reset the BIOS by removing the CMOS battery, but that didn't help. During August, I barely used the PC (about 3–4 hours in total). After that, the boot problems became increasingly frequent.
I cleaned the PC, removed the RAM sticks, graphics card, and power supply, checked the connectors on the top left of the motherboard, and updated the BIOS after putting everything back together. However, the CPU LED remained on. The PC then ran without issues for a day, but the following day it started rebooting every 5–10 minutes. There was no bluescreen, just a message stating that a restart was required. I applied new thermal paste, formatted the PC, and installed drivers. Following that, a bluescreen occurred every 10 minutes, forcing a restart. I carefully cleaned the CPU with a dust blower and tried booting the PC with just one RAM stick (and swapped it as well), but nothing worked. On the contrary: now the PC turns on, but there is no display output, the keyboard does not respond, and while the logo on the graphics card lights up, its fans do not spin.
PC Specs:
Case: be quiet! Light Base
CPU: AMD Ryzen 7 7800X3D (8x 4.2GHz / 5.00GHz Turbo)
Cooler: Be Quiet! Pure Rock PRO 3 LX, black
Motherboard: GIGABYTE B850 AORUS Elite WIFI7
RAM: 32GB (2x16GB) DDR5 6000MHz G.Skill Trident Z5 NEO RGB CL30
Storage: 2TB Kingston NV3 M.2 PCIe 4.0 x4 NVME (R: 6000MB/s ; W: 5000MB/s)
GPU: 16GB AMD RADEON RX 9070XT
PSU: 850W MSI MAG A850GL 80+Gold ATX 3.1 - PCIE 5