When DHCP fails, clients get no IP or a address (APIPA).
Troubleshooting steps:
Check if the DHCP server is running and reachable
Verify the scope has available addresses (pool not exhausted)
Check for DHCP relay configuration if the server is on another subnet
Look for rogue DHCP servers handing out wrong addresses
On Windows, use ipconfig /release and ipconfig /renew. On Linux, use dhclient -r and dhclient.