System not getting an IP may very well be the problem. Try the following for starts;
go to command prompt > type "ipconfig /release" without quotes.
This will release the IP information in the system and will disable the network card all together. Restart the computer while in this state. After restart see if the network connection refreshes the IP address. If the connection is not there, simply go to the Network settings and enable that connection.
If that fails, make sure you don't have static IPs mentioned in the settings.