If all of your software configuration checks out for the local network and you have eliminated routers or other equipment outside the local network, then you just might have a hardware problem. The components you need to check are
Network Interface Card (NIC)— Also called a network adapter card.
Network cables— Which include not only the cables that attach your computer to a hub or switch, but also any cables that are used to connect additional hubs or switches to the local network.
Hubs and Switches— These devices sometimes fail, and there are tests you can use to make sure they are working correctly.
EMI or RFI Interference— The best laid plans of mice and men don't take into account things like placing network cabling ...