Permissions Lost except for Sysadmin

SQL Server Administration
1

I am the epitome of the accidental DBA so keep that in mind. Our primary SQL Server all of a sudden started denying permissions to users to access the server (any database). The only users who can access the server are those with sysadmin permissions. Nothing has "changed" to cause this - that anyone is aware of. This has happened before and the only way to correct it has been to restart the whole server. The SQL Service was restarted and that doesn't resolve the problem.

I am not a systems person so I have few rights to do things like RDP to the server in question, check security groups via Active Directory, etc. Yes I know that makes this hard to diagnose. I can get to the databases via SSMS because I have sysadmin permissions.

I was wondering if anyone has seen this before or could point me to any literature. I have done the obligatory Google search and didn't see anything particularly germane to the subject matter.

We will be taking the server down tonight to resolve the issue but I would much prefer to identify the cause and fix the problem rather than burn down the house to get rid of the mouse.

Any thoughts?

Thanks in advance for your time and consideration.

2

are you in a windows environment with domain controller and dhcp and active directory and all?

3

That is correct. SQL 2012, Standard, etc.

Should have specified that before. Sorry.

Thank you for your fast response!

4

Are your domain controllers located on site? this sounds more like networking issues. is it a physical server or virtual, cloud or in house?
you might not have RDP perms and all but your IT department needs to own this

5

I will pass that along. I will determine the answer to your questions. I thought I would reach out and see if anyone had seen this before so I appreciate your time!