PING
From kitz wiki
PING is a utility that allows us to check if a specific IP address is online or accessible and therefore used to help troubleshoot network (or internet) connections.
It works by sending packet(s) of data to the IP address and checking the response time.
Although there are various programs that will PING an IP address for you, probably the quickest way for Windows users is to use the "ping" command from the DOS prompt. (Mac OS X and Linux users should use the Unix commands located here.)
To do this Start >>> run >>> type "cmd" Then from the prompt type "ping [IP address]".