Solving Hardware Problems
It's possible for cords, modems, routers, and other network components to fail and negatively impact your network. Make sure your router's software is fully up to date before you start hunting for bad hardware. A quick update might save you from sinking time into trial and error based investigation.
Here's an example of a hardware problem in PingPlotter. More detail about what to look for is available in Common Network Problems.
Finding the bad hardware
Systematically replace different network components. If you don't have extra hardware lying around, you probably have a friend who would love to loan you something to aid your effort. If network performance gets better after you swap out a component, chances are whatever you replaced was broken.
Solving hardware problems
If you identify which part of your network is failing, the solution is rather simple. All it takes is replacing the bad component.
By now you should know whether or not this solution fixed your problem. If this is indeed the solution, continue and we'll help you wrap things up. If you're still living with a network problem, try again and we'll try a different solution.