All my Windows 7 Enterprise Edition 64bit laptops have now failed to get an IP address from DHCP via either a wired or wireless connection. The majority of these machines are Dell Latitude 1545 but Latitude D520/530s are also affected. I have been able to resolve connectivity on the wired network by doing the following but it is also not reliable.
Set the service to run under Network Service, restart it (it fails), set it back to Local Service and restart again.
Set a manual IP address in the right range, it then connects and identifies the network successfully, the network adapter can then be set to DHCP and it will get an IP address correctly.
This is not persisted after a reboot.
THe wireless interface is able to connect correctly to the WLAN but cannot get an IP address, if a static address is set it is able to send and receive traffic but DHCP fails. The fix above does not work for any of the WLAN devices affected.
DHCP is from a variety of sources, a LInksys Wireless Router (WRT54G) and a Windows Server 2003 R2 DHCP server, they were working initially but stopped. Other devices are working fine (Macbook pro, iPhones, HTC, linux laptops etc)
I'm at my wits end as I am the only sysadmin at present and cannot afford the time to rebuild 8 or so laptops.