Mnnn..not sure what would cause that.
Somethings to check before taking it to support would be:
1) Are you using an Oracle OCI connection? (Instead of direct connect)
2) Does the bitness of your Oracle OCI client match the bitness of Toad?
3) Do the Oracle objects list when you only have one Oracle connection?
4) Go to AppDataDir in Help|About. Close Toad. Rename AppDatDir. Restart Toad. Does this correct it? (This gets rid of any cached files that could be causing the issue.
5) Got to AppDataDir in Help|About and look at ExcectionTrace.log. Are there any suspicious error stacks there that might relate to this?