Just happened to me, and turned out to be different than all other cases listed here.
I happen to have two virtual servers hosted in the same cluster, each with it own IP address. The host configured one of the servers to be the SQL Server, and the other to be the Web server. However, SQL Server is installed and running on both. The host forgot to mention which of the servers is the SQL and which is the Web, so I just assumed the first is Web, second is SQL.
When I connected to the (what I thought is) SQL Server and tried to connect via SSMS, choosing Windows Authentication, I got the error mentioned in this question. After pulling lots of hairs, I went over all the setting, including SQL Server Network Configuration, Protocols for MSSQLSERVER:
Double clicking the TCP/IP gave me this:
The IP address was of the other virtual server! This finally made me realize I simply confused between the servers, and all worked well on the second server.