Go to your WoW/Interface/AddOns/ -folder, and check if the AddOns are packed within an extra folder. This is usually the issue when AddOns aren't showing up, despite being for the correct WoW version, and installed within the right folder.
E.g. the addon might be installed like this:
WoW/Interface/AddOns/DBM-WotLK-3.3.5/DBM-Core
WoW/Interface/AddOns/DBM-WotLK-3.3.5/DBM-TBC
WoW/Interface/AddOns/DBM-WotLK-3.3.5/DBM-GUI
When the addon should be installed like this:
WoW/Interface/AddOns/DBM-Core
WoW/Interface/AddOns/DBM-TBC
WoW/Interface/AddOns/DBM-GUI
Here's a screenshot of part of my AddOns-folder for reference.