Dell OptiPlex 7040 MT shuts down under load when GPU is installed

Hello,

I’m running into a frustrating issue with my Dell OptiPlex 7040 MT: whenever I install a discrete GPU, the system shuts down under load—even at very light GPU usage (~20–30%). Without the GPU, everything runs fine. It also used to work with the GPU it just suddenly stopped working.

Here are my specs:

• Intel i5-6500
• 12GB DDR4 RAM (1x4GB + 1x8GB)
• MSI GeForce GT 730 2GB DDR3 GPU
• Genuine Dell 240W PSU (recently replaced)
• 1TB NVMe SSD

What I’ve tried / tested so far:

• GPU works fine in another PC (Dell OptiPlex 3010, Windows 7 & 10).
• Tested both PCIe slots in the 7040 → same issue.
• GPU doesn’t overheat inside the 7040.
• RAM tested individually and together → passes diagnostics.
• CPU works fine without GPU and never overheats.
• NVMe drive swapped → same issue.
• PSU replaced → no change.
• CMOS battery replaced, CMOS cleared via jumper, tested Service Mode → no change.
• Windows 7 & 10 tested → same issue.
• Minimal setup (CPU + RAM + PSU) works fine; adding GPU triggers shutdown.

✅ Tested / Done:

• GPU: works in another PC, tested both slots in 7040, no overheating.
• RAM: individual & combined → passes diagnostics.
• CPU: runs fine without GPU, never overheats.
• Storage: swapped NVMe → same issue.
• PSU: replaced with genuine Dell unit.
• CMOS / BIOS: battery replaced, cleared via jumper, Service Mode tested.
• OS: 10 tested same problem, (currently using win11)
• Minimal setup: CPU + RAM + PSU → works fine.

What should I do now? I tried everything, I updated every driver, updated bios, and everything else.