Article under construction currently. Below you will find notes that are being collected to eventually organize into a nice article.

Failed to get an IP via DHCP!

Sending discover… actually means that a network interface was found and try to get an IP for it via DHCP. So it could be:

Layer 1 issue like cable (you already checked that)
Spanning tree issue (make sure you have RSTP or configured “port fast”)
Auto-negotiation issue (try configuring static speed instead of auto-negotiation for that port)
Ethernet energy saving (see if your switch has EEE/802.3az feature and disable if possible)

Troubleshoot DHCP