Question ASUS TUF Gaming B550-Plus POST loop

[GDB007]

My specs:
Ryzen 7 5800X
ASUS TUF GAMING B550-PLUS
Gigabyte RTX3080 Gaming OC
Corsair RMx 850W 80 Plus Gold
PNY XLR8 32GB 3200MHz

Hi all,
I built this PC about one and a half year ago, and it ran well till recently. I had this problem twice, about a year ago, and then a week ago, but it was fixed by a few restarts. But yesterday it happened again, after launch computer was stuck in POST loop (mobo LED's were cycling through DRAM -> CPU -> VGA, every LED was on for 1-2 seconds). When the system starts, all the fans begin to spin (even fans on the GPU) and the RGB turns, but there is no video signal. Sometimes, instead of POST loop, only CPU LED might be always on. I've noticed, that after clearing CMOS (by taking out CMOS battery, using CLRTC and leaving computer disconnected from power source for half an hour) system starts fine, but as soon as I made any change in BIOS or just load Windows, after restart problem returns until next CMOS reset. What could be the reason for this?

What I've tried before I discovered this problem is related to CMOS:

• Start without RAM - DRAM LED is always on
• Swap RAM, run with only one memory installed on different slots, use memory from another computer, run without GPU, run without CMOS battery - always the same, POST LOOP or CPU LED lights
• Flashed different BIOS versions
• Checked the CPU for bent or damaged pins, and reapplied thermal paste
• Checked connection of all PSU cables

Thanks in advance

 

[Fix_that_Glitch]

Have you tried putting in new cmos battery?

 

[GDB007]

Have you tried putting in new cmos battery?

Not yet, all computer stores in my neighborhood are closed today, so I can't buy another one. Current battery should be ok, I've checked voltage, and it is about 3.06v which should be enough. But anyway I'll try to buy a new one tomorrow, thanks for advice

 

[Fix_that_Glitch]

Since the stores are closed did you recently install any new drivers for any device to coincide with the problem? Do you have any older restore points saved that you can try to go back to?

 

[Fix_that_Glitch]

Just to clarify, can you post if your cmos battery is removed?

 

[GDB007]

Since the stores are closed did you recently install any new drivers for any device to coincide with the problem?

No, didn't install anything new recently, not even Windows or drivers updates, one day I was just watching youtube, turned off the computer and the next day in the morning it won't start anymore.
As for restore points, I have some, but they're a few months old, might try to use one of them later

Just to clarify, can you post if your cmos battery is removed?

No, without battery post stuck on cpu led. To complete post I must disconnect power source, remove battery for few minutes (looks like 15 minutes is enough), use CLRTC on motherboard, put back battery. After that, post will be run twice, and then I can enter bios or boot into Windows. If I restart the computer after booting in Windows or change any setting in bios, I'll need to repeat everything again

 

[GDB007]

Unfortunately battery replacement didn't help. Also now computer is not starting even after BIOS reset (POST stuck on CPU LED), looks like I'll need to find a repair service...