Chances are the server name changed and the Oracle TNS listener is now trying to resolve a name that doesn't exist. You'll want to make sure those are all the same. The TNS listener is in <ORACLE_INSTALL_DIRECTORY>/product/<PRODUCT_VER>/db_1/network/admin/listener.ora
Check the section that says HOST = "something" and make sure it's whatever your server is called.
Probably also worth checking tnsnames.ora as well for the same change
Aaron