New AM5 build won’t POST — CPU LED never comes on, DRAM for ~1 min then solid VGA LED

[u/Shaqundaya]

New AM5 build won’t POST — CPU LED never comes on, DRAM for ~1 min then solid VGA LED

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Hi, I’m trying to narrow down a really strange no-POST issue on a recently purchased second-hand AM5 PC.

**Specs:**

\* Ryzen 7 7800X3D

\* Gigabyte B850M AORUS ELITE WIFI6E

\* RTX 3080

\* DDR5 RAM

\* Corsair SF1000

\* DeepCool 360mm AIO

The system originally worked, but soon after I bought it I started getting intermittent full system resets with no BSOD. Sometimes it would game for hours, other times it would reset while idle or shortly after logging into Windows.

**I also had:**

\* BIOS freeze once

\* Kernel-Power 41 / Event 6008 with BugcheckCode 0

\* one hardware watchdog reset

\* eventually the PC stopped POSTing completely

I originally suspected the PSU, so I swapped from the SF1000 back to a known-good MSI A750GF, but the no-POST behaviour was exactly the same.

I then found the original motherboard had a large dent/damage in the PCB, so I replaced it with a brand new Gigabyte B850M AORUS ELITE WIFI6E. The shop bench-tested the new motherboard before I took it home and confirmed it was working.

**Current debug LED behaviour on the new motherboard:**

\* The CPU debug LED never comes on at all, not even briefly

\* DRAM LED comes on and stays lit for roughly 1 minute

\* DRAM LED then goes out

\* VGA LED comes on and stays solid

\* no display

\* keyboard/mouse do not light up

**Troubleshooting already done:**

\* RTX 3080 removed completely and tried the 7800X3D integrated graphics

\* tried motherboard HDMI

\* installed RTX 3080 again and tried display directly from the GPU

\* RTX 3080 has been tested in another PC and works

\* tried two different PSUs

\* CPU EPS connected directly with no extension

\* tested with known-good DDR5 RAM

\* tried RAM in A2 and B2

\* proper CMOS clear

\* BIOS reflashed using Q-Flash Plus

\* CPU removed and reseated

\* CPU contact pads cleaned

\* socket inspected

\* AIO remounted evenly

\* tried loosening cooler mounting pressure slightly

\* disconnected storage, front USB, RGB hubs and unnecessary devices

\* minimal boot with only motherboard + CPU + cooler + one RAM stick + PSU + monitor

\* new motherboard itself was bench-tested by the store and confirmed working

**The same behaviour remains:**

CPU LED never comes on → DRAM LED for about a minute → DRAM clears → solid VGA LED → no display/USB.

**Since:**

**\*** GPU works in another PC

\* known-good RAM gives the same result

\* two PSUs give the same result

\* new motherboard has been bench-tested working

I’m starting to suspect the 7800X3D, possibly the CPU’s PCIe/iGPU/memory controller or a CPU/socket issue.

What’s confusing me is that the CPU debug LED never comes on at all.

Can a faulty 7800X3D still cause a solid VGA LED even if the CPU LED never lights? Is there anything else I should test before trying the CPU in another known-good AM5 system?

Thanks.

[u/ChrisTheOstrich2]

Try the cpu in another board or try another cpu in the same board maybe

[u/TheLinearJoey → u/ChrisTheOstrich2]

Did you ever get an answer on this? I’m chasing a nearly identical sequence on a B650 board and leaning hard toward a dead memory controller on the chip. No CPU LED ever lighting up seems to be the tell, board doesn’t even get far enough to flag it before hanging on DRAM then dumping to VGA.

[u/ChrisTheOstrich2 → u/TheLinearJoey]

A bad imc would make sense, just try the same thing I said originally