Pattern to record: The connection settles at 100 Mbps instead of gigabit or repeatedly renegotiates.

Separate the adapter from the network

For motherboard Ethernet, separate the physical link from Windows configuration. Record the board model, link speed and switch-port behaviour; successful Wi-Fi access does not test the wired controller. One possible explanation is that one cable pair or configuration prevents the highest supported Ethernet mode.

Link and configuration checks

1. Test a known switch and cable, inspect port magnetics and compare pre-boot and Windows detection.
2. Compare certified cable pairs, switch port and forced diagnostic modes.

Before internal work

Lightning or surge damage can extend beyond the visible network port. Forcing speed can hide a physical pair fault rather than solve it.

Verify the network path

If the checks support this cause, repair the failed pair, port or configuration and restore automatic negotiation. Verification should cover cold start, negotiated speed, sustained transfer, restart and wake-on-LAN if used.

For an assessment of your desktop computer, contact AEPC in Burswood or call 027 908 8880. Provide the model and the conditions that reproduce this problem. Workshop visits are by appointment.