No Display from GPU (GTX 1080 Ti)

PC Specs
• CPU: Intel i7-8700K
• Motherboard: MSI Z370
• GPU: Zotac GTX 1080 Ti Dual Fan
• PSU: Thermaltake Toughpower GX1 700W (non-modular)
• OS: Windows 11

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Problems
• Normally, when my PC idles, the monitor enters power-saving mode (screen off) but audio (Spotify) still plays.
• today, when I moved my mouse to wake the display, the screen didn’t turn back on.
• PC was still running (I could blindly navigate with keyboard, even shut it down).

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Symptoms
• On restart with GPU connected:
• No display signal → monitor goes into power-saving mode.
• GPU logo light turns on.
• But GPU fans don’t spin at all (on primary PCIe slot).
• When connecting monitor to onboard graphics (iGPU):
• PC boots fine, Windows loads normally.
• Device Manager only shows Intel iGPU, no NVIDIA card.
• NVIDIA driver installer → error: “No compatible hardware found.”

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Troubleshooting Done:
1. Checked display cables & ports
• Tried both HDMI and DisplayPort.
• Tried multiple GPU output ports.
• Monitor works fine on iGPU.
• No signal from GPU.
2. Driver cleanup & reinstall
• Booted into Safe Mode using iGPU.
• Used DDU to remove old NVIDIA drivers.
• Tried reinstalling NVIDIA drivers → installation failed (GPU not detected).
3. GPU reseating
• Reseated GPU into PCIe slot.
• After reseating, one time I can briefly see Windows boot logo before it goes black.
• But still no display in Windows.
4. Power connections
• GPU requires dual 8-pin connectors (from a split PCIe cable).
• Reseated power cables.
• GPU logo lights up, but no fan spin in main slot.
• PSU is non-modular, but it have2 PCIe cables, so I use another dual 8-pin connector to connect. GPU lights up but still no display
5. Tested different PCIe slots
• In primary PCIe x16 slot → GPU fans never spin, only logo LED lights up.
• In secondary PCIe slot (x8/x4) → both GPU fans spin briefly at startup, then stop (normal fan-stop feature).
• But still no display output, and GPU not detected in Windows.
6. Other checks
• Monitor + cables confirmed working with iGPU.
• PC boots into Windows fine on iGPU.
• GPU still not visible in Device Manager.

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Current Status
• GPU gets power (LED logo on).
• In second PCIe slot, GPU fans spin briefly (normal), then stop.
• No display output from GPU on either slot.
• Windows does not detect NVIDIA GPU at all.
• Only Intel iGPU is working right now.

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I don’t have spare PC, GPU and PSU to do further testing. That all I can do for now

Any advice or similar experience would be greatly appreciated. 🙏

Additional Context (Recent Behavior)
• For the past ~2 weeks, when GPU is installed, I need to press and hold the power button for 30–60 seconds before the PC powers on.
• Initially suspected case power button issue

(Now)
With iGPU display connected (GPU not driving monitor):
- GPU has power (logo lights up, PCIe LED on).
- Both GPU fans spin briefly, then stop.
- In Device Manager → GPU not detected.

With GPU connected to monitor:
- Same behavior (lights on, fans spin briefly, then stop). But no display.

No display signal at all.
• does this suggests issue is related to GPU (possible short or fault) or PSU struggling under GPU load?