Dropped table not showing up in recycle bin
It's likely that recyclebin isn't turned on. Check in your init.ora file to ensure it is. You can check your parameter:

select *
from   V$PARAMETER
where  NAME = 'recyclebin';


And turn it on at session level...

ALTER SESSION SET RECYCLEBIN=ON;


...and then try a drop.

Also, check both USER_RECYCLEBIN and DBA_RECYCLEBIN for entries.

EDIT: I see you've updated to say you are logged in as the SYSTEM user. For some reason, flashback/recyclebin does NOT work for SYS. I can't find a good reason why but it just doesn't. Create a new user and try creating and dropping a table while logged in as them. I'm sure you'll find that the recyclebin works fine then.