Multiple Issues with my server that our causing issues with users on there works PC's

It was just brought to my attention that there have been several issues with the server and employees PC apparently these issues have been going on for awhile but because I was away dealing with some family issues nobody wanted to bother me. So now I'm trying to determine that root cause of the issue and need some help in figuring everything out. I know they had to bring in some outside help about a month ago and there was not a detailed list of what that tech did. So I'm going through the event viewer log files on my Server and DNS server and I see a ton of issues that I'm having a hard time figuring out why.

Here are the error messages coming from the File Server and Domain Control Active directory
Under Applications I'm getting a lot of these.

Windows cannot query DllName registry entry for {CF7639F3-ABA2-41DB-97F2-81E2C5DBFC5D} and it will not be loaded. This is most likely caused by a faulty registration.

Windows cannot query DllName registry entry for {7B849a69-220F-451E-B3FE-2CB811AF94AE} and it will not be loaded. This is most likely caused by a faulty registration.

There'ss about another 15 more errors on that list

Under System I get these
The certificate received from the remote server has not validated correctly. The error code is 0x80096004. The SSL connection request has failed. The attached data contains the server certificate.

Now under My DNS,DHCP,DC server I'm getting these error messages

Under system
The certificate received from the remote server has not validated correctly. The error code is 0x80096004. The SSL connection request has failed. The attached data contains the server certificate.

Under DNS server
The DNS server has encountered numerous run-time events. To determine the initial cause of these run-time events, examine the DNS server event log entries that precede this event. To prevent the DNS server from filling the event log too quickly, subsequent events with Event IDs higher than 3000 will be suppressed until events are no longer being generated at a high rate.

The DNS server recv() function failed. The event data contains the error.

When I run netdiag this is what I get as well
 Testing DNS
    [FATAL] Could not open file C:\WINDOWS\system32\config\netlogon.dns for reading.
    [FATAL] Could not open file C:\WINDOWS\system32\config\netlogon.dns for reading.
        [FATAL] No DNS servers have the DNS records for this DC registered.
    Testing redirector and browser... Failed

If anybody can help me figure out what is going on it looks as though the DC got demoted possibly not really sure. If anybody could give me a hand I would greatly appreciate it. I can't get ahold of the previous tech that came out to the office to see what all was done thank you in advance.