Ok, it doesn't just stop working, something had to have happened.
Did you change something? Did you add a new game, or file, or do anything to your xbox at all? Did Xbox update your game? Did you download new content. It doesn't just stop working, something happened.
I myself had this same problem, but with a softmod, they said i had a firewall in my modem, which i called my ISP, and they don't put firewalls into the modem, so that wasn't right.
Something changed in your software, or settings.
I myself could not figure out this problem, i had gone out and switched my Xbox with another one and just did my own hardmod and used slayer's and now it works fine.
All i can say is, tell us did you do anything at all to your xbox around the time it stopped working.
What Modchip is it?
What Version Evox?
Did you unplug or change your network?
Can you/Have you tried a reinstall of the Evox Dashboard, by restoring to full retail, and then re-modding using a disc? Such as Slayers 2.6?