I am frequently troubleshooting problems in a Windows Command Prompt.  There are some functions which can be tested at a very basic level.  For example, if I am unable to connect to a server via Windows Explorer, I might jump into a command prompt and try to ping the server. 

ping [servername]

If you receive a response like this one, you've established the server is on the network and you can reach it --

Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
Reply from 127.0.0.1: bytes=32 time<1ms TTL=128
Reply from 127.0.0.1: bytes=32 time<1ms TTL=128

If you the response is:

Request timed out.

You cannot reach it.

Now let's say it's an SMTP mail server and you're able to ping the server but you're unable to send email.  Assuming the server is using the default port of 25, you can check the server by making a connection using Telnet via the command line with the following:

telnet [servername] 25

Or if you were testing connectivity to a www server on port 80:

telnet [servername] 80

Depending on whether or not you get connected, you can narrow down the problem.

But now let's say you're on a Windows 8 machine or a more recent Windows Server version where Microsoft decided to turn off Telnet by default.  You can enable Telnet via an elevated Command Prompt using the following command:

pkgmgr /iu:"TelnetClient"