I've got a 1 year old Dell laptop running Windows 7 Pro 32 bit.
Last week, the PC started refusing to obtain an IP address via DHCP, but this only happens on the Wired Ethernet connection. The PC is assigned an APIPA address in the 169.XXX.XXX.XXX range. However, if I manually assign an IP address, the connection works fine.
If I switch over to wireless, the PC is able to obtain an IP address via DHCP just fine. The WAP which it is connecting to is on the same network as the DHCP server (a Netgear DG834 ADSL Modem router).
The network is a simple Windows network (no domain, active directory, etc).
I've tried connecting the laptop to different network points around the office, and even directly into the ADSL router, and it doesn't make a difference.
All indications suggest that there is something wrong in the Windows Networking stack on this machine.
UPDATE: It's worth pointing out that we changed the router (and thus DHCP server) from a Siemens Gigaset to the current DG834 router on the same day. No other machines on our our network of 40+ devices were affected by the change. It's possible that the problem could be related to this, though I can't see how.