Browse Host is pretty unreliable... one minute you won't be able to browse & the next you can. Always try to browse a host with chat enabled (you'll see a smiley in the Chat column). You should also have chat enabled (tools > options > chat)

You'll find that you have the greatest chance of success if you're trying to browse a LW or FW (shows as Snow) host. Try using right click > browse host, as well as the Browse Host button.

There seems to be a fair bit of luck involved in being able to browse