User Name/Password - Connectivity Issue

I'm on a mac mini - mid 2011. 10.10.2

I just updated my os and security update. I now cannot connect to the mac mini across the network, although airdrop still works. I was using 'Connect to Server' under 'go'. Also, when I'm in Users and Groups, my user name and password will not unlock to make changes. Can anybody help?

Thanks for your time in advance.