PC Restarts Itself, then Stuck on POST

Hi, my sister's PC has been seriously unstable over this month. PC oftenly restarts itself and then stuck on POST. At first, this is only happening max. once in a day. Now it got worse, I can't even use Windows more than 30 minutes, as the PC will restart again and stuck. The specs are :

AMD Thuban 1090T
MSI 890FXA-GD70
2x8GB Corsair Vengeance DDR3
AMD Radeon RX 550 4GB
WDC Green 2TB
Enermax NAXN 500W

The BIOS stuck with either "Initializing USB controller" or "Initializing USB controller...Done", Normally, IIRC, after showing those info, POST checks RAM and HDD. So I did some tests :

Things I did :
1. Resetting RAM on all sockets, this including only use 1 stick on each socket
2. Use different GPU card (Radeon R7 260X 1GB)
3. Clean up disk space in all partitions so the bar on Windows Explorer stays on blue
4. Unplug the SATA data cable from HDD (No disk in the PC) and let the PC boots with Ubuntu 18.04 live USB

It didn't solve the problem, even when I "Try" Ubuntu from live USB, PC seems to lose power and stuck again on POST. When this problem occurs, the LED debug code on mobo shows "38" (or "3B"?). I'm positive this is not a temperature as when I start the PC anytime it goes around ~40c.

Next component I suspect could be the issue is the PSU, but it's relatively new (2 years old) so I doubt it and it seems other components (LEDs, system fan, USB ports, etc) running just fine. So I'm stuck with the processor or mainboard, both bought from late 2010 (8yo), but I don't have any spare processor and mainboard right now. Both processor and mainboard temperature sensors, from what I can see in HWMonitor, is around 40c-50c.

Could processor/mainboard be the issue? And how to determine that either of them is the problem?

Thanks in advance :)

Check Capacitors for blown ones , Service for dust , Check for bad sectors , Try to free some disk space , Do a malware scan using Malware Bytes and Rogue Killer , Check to see if CPU is running at high % of utilization , Check to see if Microsoft is trying to kill your PC by silently installing faulty drivers you didn't ask for uninstall them then tick No to updating Manufacturer's Drivers and Apps and install them on your own , Take out parts one at a time to see if one got defected and is causing trouble , do an in-place upgrade for windows using Windows Media Creation Tool .
Yep , about that routine .
good luck

Hi guys and thanks for the replies.
@Caledon Ken
I forgot to mention that I monitor the mainboard speaker, One short beep when it successfully POST, and no beep if it's stuck. I'll buy CMOS battery at my local shop, like your suggestion. And after take a look at the mainboard, I can't find any capacitor that looks like malformed.

@nIGHTmAYOR
I already cleaned up the case, fans, etc. Also already monitor HDD health using Crystal Diskinfo ("good" condition) and scan for malware using Malwarebytes (found 2 malwares). CPU and HDD usage are high after successfully boot into Windows, with Windows Superfetch and Windows Defender dominate the usage.

I'm sorry but I already mentioned that even I don't use any HDD (boot into Ubuntu w/ live usb) this problem still occurs.

I'll report back later, thanks for helping me :)

cliffflip said:

Hi guys and thanks for the replies.
I'm sorry but I already mentioned that even I don't use any HDD (boot into Ubuntu w/ live usb) this problem still occurs.

Ok if so might sound like a case of a failing PSU , check to see if your power socket is not sparking and also if possible try replacing PSU by one known to work ?

Turns out it was the mainboard. I brought my pc to my local shop, and when they swap the mainboard, along with my other components, it works.

Thanks for your help guys :)