N1996 Motherboard Manual- -

The manual clarifies that the single PCIe x16 slot operates at x8 electrical when both PCIe x1 slots and the onboard VGA are active. For full x16 speed, disable the onboard VGA in BIOS (set "Primary Video Adapter" to PCIe).

This indicates a CPU overheating condition. Verify the heatsink fan spins freely. The N1996 has a thermal shutdown threshold of 95°C. Reapplying thermal paste usually resolves this. N1996 Motherboard Manual-