Debugging is simple if you know how to isolate the problem...
Below are steps you can take to pinpoint the source of your problems.
Assumptions:
Open a commandline console and type:
ping [IP address or name of host] e.g. Ping 192.168.1.1
If it replies with "Request timed out" instead of "Reply from 192.168.1.1" you must check your network connection
Windows:
Linux: