Team Foundation Server suddenly failing to connect (Error: TF400324) - sql-server

Question

After using Team Foundation Server (TFS) for years, we suddenly lost the ability to connect either through Visual Studio (VS) or via URL. To the best of my knowledge, no changes were made to the virtual server that supports TFS.
In VS the error is:
TF400324: TF services are not available from server... Unable to connect to the remote server...
If I use the {server}:8080/tfs or localhost:8080/tfs url in a browser it tells me the connection was refused.
In the SQL Management Studio both the Tfs_Configuration and Tfs_DefaultCollection databases appear to be connected, and show a "Ready" status. In the TFS Administration Console the DefaultCollection state is "Online".
Perhaps the best clue is that if I use netstat to see which ports are in use on the server, port 8080 is not listed at all. Is there a listener service that needs to be started?
I see that the following services are currently disabled: UPnP Device Host, SSDP Discovery, Internet Connection Sharing, SSDP Discovery, Internet Connection Sharing, Smart Card, Routing and Remote Access, Net.Tcp Port Sharing Service, and Computer Browser.
Of course, we have tried a reboot to no avail.
Any troubleshooting suggestions will be much appreciated, as this has begun to impact our productivity. Thanks in advance!
Edition: TFS 2015
Version: 14.114.28805.0 (Update 4.2)
Update:
I should mention that the firewall has been disabled in attempting to diagnose the issue.
Also, there are errors associated with TFS in the Even Viewer, but they are not at all clear. Here are is a snippet:
VssRequestContext.HostManagement.Microsoft.TeamFoundation.JobService.Extensions.Core.IdentitySyncJobExtension.Run:1
Registry.TeamFoundationRegistryService.Write:1
Default.SqlResourceComponent.Execute prc_UpdateRegistry ds:LT-TFS2
db:Tfs_Configuration:2 Default.SqlResourceComponent.Execute:-3
Registry.TeamFoundationRegistryService.Write:-3
GroupComponent.SqlResourceComponent.GetGroupsToSync:3
GroupComponent.SqlResourceComponent.Execute prc_GetGroupsToSync
ds:LT-TFS2 db:Tfs_Configuration:3
GroupComponent.SqlResourceComponent.Execute:-4
GroupComponent.SqlResourceComponent.GetGroupsToSync:-4
GroupComponent.SqlResourceComponent.ReadGroups:4
GroupComponent.SqlResourceComponent.Execute prc_ReadGroups ds:LT-TFS2
db:Tfs_Configuration:4 GroupComponent.SqlResourceComponent.Execute:-5

Answer 1

SOLVED!
I found that the TFS site was disabled within the IIS Manager. When I tried to enable it, it reported that the World Wide Web Publishing Service was disabled. Enabling both resolved the issue.

Answer 2

This error is usually related to TFS cache. You could give a try following below steps:
Close all instances of Visual Studio
Open the Task Manager and check if any TFS Services are running. Select each of them and click on End Process Tree
Browse to the folder %LocalAppData%\Microsoft\Team Foundation\ and then select the folder with your TFS version and go inside
the Cache folder. for example, the path was
%LocalAppData%\Microsoft\Team Foundation\x.0\Cache and it should be
the same on your machine with the difference of the TFS version folder
name.
Delete everything in that Cache folder.
Start Visual Studio and run it with Admin mode.
Besides, in case of your TFS is configured with self-signed TLS/SSL certificate.
If this is the case, you need install that certificate to the Trusted Root Certification Authorities store on the client machine, where you have VS.
For this scenario, you could refer this answer.
Moreover, please also check if there are any errors in the event viewer in your TFS server. This may help to narrow down the issue.