Have you tried in the Lightroom menu to go to File/Open Recent?
If it can't be found under recent do an OS search.
On Windows click the start button and type into the search field:
On Mac click the spotlight search icon (magnifying glass icon top right from your desktop) and type:
You should get a list of all the catalogs and can double click on the one you want to launch it.
Yes, and they are not there.
99jon: I have already done those searches and unfortunately nothing comes up.
If that's the case, you need to find the backup of this catalog and restore it.