Removing the database implies that you manually delete the content of a folder stored on your Windows drive because the software does not provide a button or something similar to remove the entire database. In order to remove the directory, you should first close the software, then open Windows Explorer or My Computer. With Tools > Folders Options > View > Hidden Files and folders check Show hidden files and folders from the main menu. Then use My Computer navigate to your system partition (usually is C: ) and go to
\Documents and Settings\USERNAME\Local Settings\Application Data\ACD Systems\Catalogs\120\Default\ (where USERNAME is your computer account) and delete all the files. You will also clear unrated albums from the database by doing this operation. Then start the software again and it will be like new one.