1) Goodies -> One Click Installs. See if the previous installation is listed under Modify/Delete existing software (in both Easy and Advanced sections) If so, then delete it.
2) Use phpMySQL to log into the database and Drop all tables. Or delete the database in the Goodies -> Manage MySQL section. Or create a new database. And use/change new passwords!
3) One-Click a new WordPress installation (with a new username and password). And stay away from sketchy plugins. Were you using any additional plugins last time?
Good idea. They could be exploiting one of your other sites to get into your home directory.