The first step to take when troubleshooting connectivity (besides physical connectivity check) is to try and ping each device, and the devices in between (if applicable). You should also check that both devices are on the same subnet, and are pointed to the same gateway (if they are different gateways, you'll need to setup a Static Route in each gateway to the other device).
If you can ping both devices, your next step is to check for firewalls. These are likely on each computer, as well as the device used to bridge the LANs (depending on how exactly you've got your bridge set up).
If your bridge is something like a WiFi bridge, or other hardware-based routing method, it may use NAT and a firewall, which you'll have to configure. If it's software-based, like Hamachi, you'll need to make sure that each computer is actually using that virtual network adapter to establish the connection. You can configure which network adapter applications choose by default by going to Network Connections -> Advanced -> Advanced Settings. Then look at the Connections list, and re-order them so that Hamachi (or other software bridge) is on top. You may need to reboot for changes to take effect.