I've been helping people that come through the "Support" channel I created as much as possible, and this is a very common issue for new testers.
Something I should state before we start as I've noticed some people not doing so is that it's best to close down any programs while doing this (except for HoN if you're chatting with me to get help on this). After I give you instructions though you should shut down HoN, do as instructed and then restart HoN.
The first step to ask yourself is have you TURNED OFF all firewall, antivirus, and any other security software. NOTE: not disable turned off. If necessary use the task manager's processes tab to close the processes that correspond to your security software.
If step one didn't work the next thing to check is what ethernet adapter you have (for those that don't know an ethernet adapter is the hardware you use to connect to the internet and your local network). To do this in Vista simply open you start menu and type in "device manager" where it says "Start Search". In XP the quickest way is to right-click "My Computer" and click "Manage" and on the left side click on "Device Manager".
Now that you're in the device manager click "Network adapters". If you have the Atheros L1 Gigabit Ethernet 10/100/1000Base-T Controller then we've most likely found your problem. Right-click this device and hit properties and check your driver version on the "Driver" tab. If you don't at least have version 2.4.7.10 then that's your problem. Click this sentence to directly download the 2.4.7.10 driver. Important note: you DO NOT need to install the utility that comes with it to get HoN's game list to display properly.
Finally, if the above steps haven't straightened out your game list there might be an error showing in the console. You can either view this by clicking control + F8 after trying to refresh the game list or you can view the console.log file in the [Vista] <driver letter here>:\Users\<username>\Documents\Heroes of Newerth\game directory and [XP] <driver letter>:\Documents and Settings\<username>\Documents\Heroes of Newerth\game directory. It's better to view it in game just after you tried refreshing the game list because the errors will show in red. The error I've been told about a few times is something like a chp data error or something like that. I don't understand this error and you should report it here if you receive this error in your console. Hopefully the appropriate member of the dev team can then aid you.
If none of the previous steps help please stop into the "Support" channel in the game client and I will try and help. S2KingKtulu is around sometimes, but he's often busy so don't spam him as it will likely not help in getting his attention.

Thanks for reading and I hope this helps some people.
S2KingKtulu redux:
Thanks Avi, Im going to add some links for common issues and reported software conflicts.
Avira Antivirus with WebGuard:
http://forums.heroesofnewerth.com/sh...1&postcount=17Exceptions have to be specified.
http://img140.imageshack.us/img140/3165/avirar.jpgOutpost Firewall
http://forums.heroesofnewerth.com/sh...83&postcount=1Linux / Proxy related
http://forums.heroesofnewerth.com/sh...&postcount=295