-rascal-

It looks like 4x DIMMs is still a bit of a hassle, as of... 2 months ago. Some people are having some luck with 4x DIMMs, but the speed is significantly reduced. I agree with @OddOod, it likely needs to be fixed/improved within the CPU Integrated Memory Controller (IMC) itself.

You won't get accurate temperature reading, it will basically give you the air temperature coming off the heatsink. It's going to be A LOT lower than actual CPU temperature. HWMonitor can give funky readings....I've personally switched to using HWiNFO for all my systems, including my Ryzen 5800X rig. The motherboard should support Ryzen 5000 series out-of-the-box, but you can check for any new BIOS updates. If you suspect a BIOS setting is wrong, possibly, use the 'Load Defaults' option.

I would double check the mounting. When you reinstalled the CPU Cooler, did you tighten the 4x screws gradually (e.g. in a 'X' pattern) ? @PcBeExpensive Made a good point about the Sensor / Software.

Did you re-use the thermal paste + cooler from the Ryzen 4500? If you take the CPU cooler off, you want to re-apply the thermal paste. Next step is to make sure the cooler is mounted properly. The Ryzen 5500 should not be getting that hot, even with the stock cooler.

If the PSU is dead / dying, you don't really have a choice. Especially if you need the PC up and running ASAP, too. I would NOT recommend that you try to "self diagnose / self repair" a malfunctioning PSU, too.

Ryzen 5600 does NOT have iGPU. The HDMI / DP ports on the motherboard does nothing. @Dixel if you can borrow another graphics card or something, to rule out a faulty GPU. The Red LEDs on the XFX graphics card only comes on during two possible scenarios: PCI-E power cable not connected / missing Voltage through the connector is too low (e.g. PSU / connector issue) So the other item to check is the PSU - see if that has started to go bad, etc.

There is a possibility that the PCI-E X16 slot may be damaged, too. You'll have to get a friend or a shop to help check each component (e.g. CPU, RAM, GPU, etc).

That's normal. The debug LEDs / Q-LEDs are supposed to cycle through CPU-RAM-GPU-BOOT. It's checking if each major component is working, and will STAY on the item that's causing POST / Boot problems. The checkboard display on the bottom of the screen... that is NOT a good sign. That is some sort of GPU artifact - signs of a failing GPU.

No Blue Screen or anything? How much storage is left on the SSD? I would say to check the health of the SSD and the RAM first, then the RX-590.

That is very likely a defective LED within the fan hub. It should not behave like that.

CPU frequency sitting at ~1700 MHz is abnormal. That's 1/2 of the 3.4 GHz Base frequency....it's like the CPU is running on idle mode. Also explains why the CPU temperature only peaks at 40*C. EDIT: Found his result(s) on the 3DMark website. Links: https://www.3dmark.com/fs/31722082, https://www.3dmark.com/fs/31721931, https://www.3dmark.com/fs/31721815

Yup I think PCPartPicker made a mistake. The motherboard has: The case has: 1x USB 3.2 Gen 2x2 (e.g. USB-C) cable 1x USB 3.2 Gen 1 cable You shouldn't need an adapter...

Essentially, yes. A higher-end Gen3 or Gen4 SSD with more storage over a Gen5 SSD with lower capacity. Also, Gen5 SSDs can run HOT when you push it. Gen3 and Gen4 typically runs cooler. Checking local pricing for me... A Gen5 Crucial T700 2TB is $529, the 4TB model is $899.99... Gen4 WD SN850X 2TB is $234.99 and 4TB is $434.99 Gen4 (tier below the SN850X) WD SN770 2TB is $189.99...

If you are just chasing for faster load times, going from Gen3 -> Gen4 -> Gen5 is not going to be noticeable faster. Going from HDD -> any form of SSD (even a SATA3 SSD) is a VERY significant change. In the chart @Electronics Wizardy linked, the Crucial T700 is a Gen5 NVMe SSD. The WD SN580 is a lower-end Gen4 NVMe SSD. The difference is 0.9s. You are not going to see... 33s vs 5s.

Either go up to the 6800XT (or better), or as someone already mentioned, 7800XT or 7900 GRE.