Question PC doesn't POST after switching to dedicated gpu

[ltsNotMike]

Hello everyone.

Before describing my issue let me introduce you to the components:

CPU: Ryzen 5 5600G
Motherboard: ASUS TUF GAMING B550-PLUS
RAM: Corsair 16GB (2x8GB) 3200MHz CL16 Vengeance RGB PRO SL
PSU: Thermaltake Toughpower GF 750W 80 Plus Gold
Boot drive: WD 1TB M.2 PCIe NVMe Blue SN570
Monitors: MSI Optix G241 + EIZO FlexScan S2202W

I built this pc some time ago (like 6 months). After assembling it I had some problems with getting to post. The motherboard was lighting up LED for GPU problems. The CPU was first hand so I was confused. I refitted everything and checked if everything sits properly. That did not help. I switched monitors from the new MSI (HDMI to HDMI cable) to some old EIZO (DVI-d to HDMI cable). The computer posted without a problem. I switched to MSI again and it posted. After that, it worked without a problem for some time. The only issue was restarting the PC from windows. When I restarted the PC with the Windows button it wasn't posting and I had to use the physical reset button on the case.

Now, forward to the present. I bought Gigabyte GeForce RTX 3060 Ti. I put it in and I got no post. I removed it and tried to post with integrated. No post. I'm using this "new MSI" monitor. The error on the motherboard is the same - LED for GPU problems.

Every suggestion would be great. Thanks in advance for all your input into this case.

 

[ltsNotMike]

UPDATE:

I managed to get a post. I removed the battery from the motherboard, unplugged the PC from the wall, and left it for some time. After that, I removed RTX, plugged it into EIZO and it posted and booted to windows. I installed drivers for RTX and tested it on some games. After some time I switched off the PC, and now it's not posting again. No clue what is happening so any suggestions will be appreciated