If you are unable to access the web-interface on your miner make sure you are using the correct ip address, if you have not changed the ip address of your miner it should be 192.168.1.99. You will also need to make sure your computer is on a compatible subnet, if your computers IP is not between the addresses of 192.168.1.1-192.168.1.254(it also should not be 192.168.1.99 since that will conflict with your miners IP) then you will not be able to access your miner without reconfiguring your computers network interface. You temporarily change your IP to something that will be compatible with your miner such as 192.168.1.254. You should then be able to access your miners control panel on 192.168.1.99.
On OSX you would open Network Settings under System Preferences.
You would then enter a temporary IP address.
and hit "OK"
Try accessing your miner by typing 192.168.1.99 into your web browser. If this is successful you should see the main login page. The default password is "root".
Next under the Network -> Interfaces tab select select edit under the WAN interface.
You should now see the network settings menu for your miner.
From here you have two options, you can either configure a static IP or you can set your miner to DHCP, if you know how to locate a device in the devices list in your router that may be easier. To set your miner to DHCP select "DHCP client" from the Protocol drop down menu.
Next Press "Switch Protocol" and then "Save and Apply.
Your miner will then change IP and you will need to locate it by either looking it up in your routers devices list or using an IP scanner utility.