The 88 Reboots Mystery

Date: 2025-09-08 Duration: Several hours across multiple sessions Issue: Random system freezes at login, 88 reboots in 3 weeks Root Cause: PCIe Gen4 timing issues on older hardware

The Symptom

Happened randomly. Sometimes three times in a row. Sometimes not for days. Over three weeks: 88 reboots. I counted.

The RTX 4070 Ti was new. The i7-4790K motherboard was not. They weren’t getting along.

The Investigation

Checked logs. Kernel panics. GPU driver failures. PCIe bus errors. Nothing consistent.

The pattern: it always happened at login, after the GPU had to render the desktop. Something about that transition killed the connection between GPU and system.

The Theory

PCIe Gen4 is faster. The 4070 Ti defaults to Gen4. But my motherboard only supports Gen3. The negotiation should fall back gracefully.

Should.

Old motherboards have timing quirks. The Gen4 negotiation was working most of the time, but occasionally the timing window was too tight. The GPU connected, the system came up, and then somewhere in the handshake, things went wrong.

The Fix

BIOS changes:

1. Forced PCIe to Gen3

No more negotiation. No more “let’s see if Gen4 works.” Locked it to what the motherboard actually supports.

2. Disabled IGD Multi-Monitor

The integrated GPU was creating additional confusion. With an RTX 4070 Ti, I don’t need the Intel HD Graphics interfering.

3. Set Primary Display to PCIe

Made sure the system knew: GPU is king. Don’t try anything clever with the integrated graphics.

The Trade-off

What I lost:

PCIe 4.0 bandwidth (about 1-3% FPS in bandwidth-heavy games)
Flexibility in display configuration

What I gained:

A system that doesn’t reboot during login
Predictable hardware behavior
My sanity

The bandwidth loss is theoretical. The crashes were very real.

The Immediate Consequence

Fixed the reboots. Broke a monitor.

Five minutes after the BIOS changes, my right monitor went dark. Still detected by the system but showing nothing.

xrandr --output DP-2 --off
sleep 2
xrandr --output DP-2 --auto

It came back. But now I had a new worry: had I traded login stability for display stability?

The Fourth Monitor

While debugging, I noticed xrandr showed four monitors. I only have three.

HDMI-A-1: 1920x1080
DP-1: 1920x1080 (primary)
DP-2: 1920x1080
DP-3: 640x480 (0mm x 0mm)

DP-3 with 0mm physical dimensions. That’s not a monitor. That’s my Valve Index VR headset, sitting in standby. The system registered it as a display but couldn’t communicate with it properly because VR headsets don’t behave like monitors until you launch SteamVR.

Mystery solved. Three real monitors, one VR headset pretending to be a low-resolution display.

The RAM Bonus

While I was in the BIOS, I noticed XMP wasn’t enabled. The DDR3 was running at 1333 MHz instead of 1867 MHz.

Fixed that too. 40% more memory bandwidth. Should have caught that years ago.

The Final State

PCIe Gen3 forced (stable)
DDR3-1867 via XMP (faster)
IGD disabled (cleaner)
Login freezes: eliminated
Monitor that occasionally needs a refresh: acceptable

The system has been stable since. No more coin-flip logins. The right monitor went dark once more, fixed with the same xrandr commands. That’s a trade I’ll take.

What I Learned

Old motherboards and new GPUs are a gamble. PCIe should be backwards compatible. It mostly is. But timing edge cases exist.

Force the lowest common denominator. Auto-negotiation is great until it isn’t. If you know what your hardware supports, tell it explicitly.

Check your RAM speed. XMP not being enabled was a performance tax I’d been paying for who knows how long.

VR headsets appear as monitors. If you see a mystery 640x480 display, check if you have a headset plugged in.

88 reboots. One BIOS setting. Sometimes the fix is exactly as simple and as annoying as you’d expect.