SYMPTOMS:
1. SharePoint front end or application server is not working (ie .net error msg)
2. You have an application error something like parameter incorrect server
3. Errors in Event Log about the server not being part of the farm
4. Timer jobs in Central Administration are paused for a specific server in the farm
RESOLUTION:
Check the following registry key and change if it contains an incorrect value (Note: it's best to copy value from another server in the same farm if need be)
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\15.0\Secure\ConfigDB
Key: dsn
Type: REG_SZ
Incorrect Value:
Connect Timeout=30
Correct Value Format: (Note: You can also copy the correct value from the same registry key of another server in the same farm)
Data Source=YOUR_SQL_SERVER_MACHINE;Initial Catalog=YOUR_SHAREPOINT_CONFIG_DB_NAME;Integrated Security=True;Enlist=False;Pooling=True;Min Pool Size=0;Max Pool Size=100;Connect Timeout=15
No need to restart the server. It will automatically become a member of the farm again. But you can restart the server if it gives you a warm fuzzy, it was already "down" anyway. You will notice in CA that the paused timer jobs will start processing again.
