"Start from the beginning" Method

This is a Basic Network Topology.

Check all phisical connections to make sure nothing came unplugged 

Test every connection and cable starting from the Modem, to the Router, to the switch's, then to the end wall plate. Does it pass?

Start at the beginning. 

Internet signal comes from the modem 

The Router is next in line. 

This Routes all Data Traffic to the right IP addresses and the right Networks 

This also provides Wi-Fi 

From the Router, 1 Uplink cable goes to a Switch.

Another port might go to another Switch. 

Switches are there to give more Ports, for more stuff. 

From the Switch to Patch Panel. 

From there a Data Drop is Routes to the wall jack, or biscuit jack.

Test all cables. See if one's bad