Primery Domain Controller Not working Properly

Hi,

We have two windows server 2012 domain controller.My primary server not connect network more than 1 month.After connected the network DNS and Replication not working.we are created user account in primary server and i try to logging PC using this account ant set primary server DNS in this PC can't logging.I created user account in my secondary domain and i try to logging using this account and set secondary domain DNS it's working properly.

What is the reason.how can current my primary server.

Thanks.