Sometimes when Kith and Kin Pro V3 refuses to see your database, it could be because the database is from an older version of Kith and Kin Pro (V1 or V2). Nothing in Kith and Kin Pro V3 will indicate this since the older databases are completely incompatible; see: Conversion of old V1 and V2 databases.
It's easy to check the version of your database. In Windows, click on "Start | Computer". Now you will have to navigate to your database folder. By default, Kith and Kin Pro V3 databases are stored in "C:\KKPro3Data" so in there you should find a folder with the same name as your database, eg. MyFamilyTree. Open the MyFamilyTree (or whatever) folder and you should see a large number of files - these together make up your database. Now, your computer may not be set up to display the full file names; the extensions (the bit after the last dot) may be hidden for some. To display all file extensions, click on "Organize | Folder and Search Options | View" and take the tick/check out of "Hide extensions for known file types" and click on OK.
If your database folder contains the file Aliases.DAT
then it is a V3 database
If it instead contains Aliases.DB
then it is either a V1 or V2 database
If you need to differentiate between a V1 and V2 database, only V2 databases
will have a UFields.DB