If you have a Broadcom NIC firmware that is very old, this will sometimes happen.  Update the NIC firmware and drivers, then your network connection should be restored.
PowerEdge T300, Server 2008 (x64) We added two drives to our server and in an attempt to aviod restarting, I installed the OpenManage software to allow us to provision them as a new RAID1 array. I did the installation over remote desktop and when it got to "starting services" the server's network connection dropped.  We could not access the server over the network at all. Someone in the office did a hard restart (instead of trying to log in on the console), and when the server came back up, the network was still not accessible.. Someone logged in on the console, opened the network connection properties IPv4 properties and clicked apply and it started working again.. We were hoping that it was a one time issue, but we restarted twice since than and each time the network would not come up. Is there some component of OpenManage that would cause this problem? My boss does not want me to remove it until we actually try to figure out what the problem is. Any other ideas of what to look at? The fact that it first happened during the OpenManage installation points to it being the problem, but I can't be 100% sure.
OpenManage causes network not to come up on startup