ASUS Z170 Pro Gaming strange LED sequence

[Fr0sty420]

Hello,

I am wondering if anybody could help me to find out what might be going on with my motherboard. I have a computer purchased about 5 years ago, the parts were:

- Intel Core I7 6700K Skylake CPU

- 16GB HyperX 2933MHz RAM

- Asus Z170 Pro Gaming motherboard

- Palit GTX 1070 GPU

- Samsung 850 evo SATA SSD

- 2TB HDD

- 700W PSU

the computer was running smoothly without any issues, but recently, I have purchased a Gigabyte Vision RTX 3080, an 850W Gigabyte PSU, an ADATA A2000 M.2 SSD and a new case. I disassembled the old computer, didn't manipulate the CPU or it's cooler, and just installed the mobo with the cpu and all the old drives, along with the PSU, GPU and the M.2 SSD in the new case. My PC was booting without issues, but after a few days I noticed a weird booting behavior. The status LEDs on the mobo each light up in sequence, stay on for like a one second, and then the system normally boots, but other times, the VGA or BOOT_DEVICE_ID LEDs would stay on or blink along with the other LEDs, while I see only a black screen with  a flashing white cursor jumping around the top left corner of my screen. Sometimes, after a few seconds of LEDs blinking and white cursor flashing, the system boots, sometimes it goes through this "sequence" a few time and then displays the BIOS screen (the screen where I can actually change settings, not the "Press Del to enter setup"). When that happens, I just hit Save & Reboot in the BIOS screen and then the computer normally boots, sometimes with more flashing lights.

I should mention, that while I'm not a miner, and I got the GPU for gaming, I do mine crypto when I'm not using the computer or I'm not doing any demanding work, and the GPU temps on the memory were getting close to 100 C, so I actually swapped the thermal pads and thermal paste on the GPU (which boosted my hashrate instantly by 20MH/s lol).

But as I said, am not a miner, and now I am really scared about what's going on with the computer, the card cost me a fortune (didn't buy from scalpers tho, bought on Alternate.de and shipped to my country). The behavior seems to be random, and didn't happen for the first few days after building the PC. Sometimes I get the BIOS screen, sometimes just the white cursor, sometimes a normal boot. I don't understand why it boots into the BIOS randomly, or why do I see the flashing cursor. If one of the LEDs stayed on and the computer didn't boot, I would at least know where the problem is, but as I said, the computer always boots in the end, which makes my anxiety for my precious GPU skyrocket.

Could it be a weak PSU causing the erratic behavior? Is the mobo dying? Or have I damaged my the GPU somehow, perhaps with the high temps? (sometimes, its the VGA LED that stays on) Or does anybody have an idea what this random behavior could be indicating? The problem is not that the PC wouldn't boot, it's just that I'm scared whats going on and I don't want to damage the GPU

Thanks a lot for any ideas