I just purchased 4 Dell Optiplex 960 computers with WIndows 7 x64. I am having this issue on all 4 machines. Intermittently the computer disconnects from the network and also at times it will show that it is a 10mb connection. I updated the drivers to 11.5.10 dated 12/10/2009. The error in the event log is source: e1kexpress Event ID 27 "Network link has been disconnected." The workstations all connect to a Dell switch.
I spoke to Dell and they have no clue.
Help is appreciated.