We're having a simialr problem.
We were given a pair of comtrend ethernet adapters to use with our BT Vision box, but ended up not needing them for it. Now we're trying to use them upstairs to get better connection on laptops etc, but they won't connect to the internet from anywhere.
I did a search online and managed to get a copy of the manual for the earlier (white) version of the adapters, and have followed the instructions for resetting to factory defaults. All the lights are now correct so they seem to be set up and synced with each other properly, but when connected to a computer or laptop the connection status says "Unidentified network, no internet access".
I tried following the instructions for manually setting the IP address, in order to change the actual device settings via the WUI but that just didn't work at all. The intructions were in reference to windows XP and we all have windows 7 which made a specific part of the insturctions very difficult to follow correctly as the interface had several extra options for IP settings which aren't in the comtrend manual. Additionally the free software the manual tells you to download has also been updated, and doesn't display as the pictures show which made it even harder to know if you're following the instructions properly.
Overall it's just disapponting... they're supposed to work "out of the box" so I really don't get why they require such a fuss and stress over, even after following the manual (as best as possible) and being reset to factory default multiple times.
I was given a pair of these at the weekend.
I found the same instructions and set one to master which is connected to my router and one as a slave which is in a shed (an IP cam for wildlife).
I didn't change anything via the internal webgui and they are working a treat.
Hope this helps if only to let you know they do work.
One thing to check - Can you see the two devices in your HH3 list of attached devices?
The MAC addresses are on each device label.