Hi,
let's take a step back and see all the steps that you need to do.
i hope that you will not be dissapointed by the number of steps or by the manner that i written but i think there are a like a walk trough.
1 check physical connections (cables, switches etc)
2 get a computer connected from the same switch as the wan interface and try ,A ping google , B open a webpage, C check for proxy setting and write them down, D write down the DNS, Gateway, IP class etc etc
3 Get in ebox and configure the dns under Network
4 Get to interfaces under Network and check the eth0 (wan) settings to be correct
5 add a temporary roule to allow anything from internet to ebox and anything from internet to lan
(any to any roule)
6 check you apt source file. see if you have the right sources in that file
(check in /etc/apt/sources.)
7 run a ping command to google from ebox console(not web gui)
8 try to run apt-get update .....
if it still does not work
9 check again all the above
10 come back here with details.
Best regards and best of luck
Bogdan