There are various types of network problems that occur in an organization,which results in inaccessible devices,performance degradation, etc.These can be classified as:
Network Hardware failure : Includes faulty devices like switches,Ethernet cards,improper cabling etc.
Network configuration problems : Includes issues related to improper configuration of protocols
Malicious code : Includes issues as a result of the presence of worms/viruses on the network
In order to troubleshoot network problems from scratch you need to start checking by hardware – ie,physically check network cabling,network cables crossovers over electric cables,quality of switches routers etc. If the problem lies in the hardware this method of tracking is reasonably straightforward.