there are many steps that can help troubleshoot the network.
first start with checking physical components such as cables , NIC etc.
secondly make sure that your diagram is correct in the way of IP addresssing using the correct subnetmask etc.
thirdly you need to check that all the interfaces are assigned the correct configuration that you planned for it.
make sure no shutdown command is applied into all the interfaces.
then try to ping , traceroute to determine where the problem located.
finally you need to include more information about your network if you need a more accurate info for troubleshooting your network.
i hope this helps