Sure, you look for the correct library path? Default library path is "Calibre Library" and "Calibre Calibre" as library location sounds for me a bit strange. (only a guess in the blue sky)
As fare as I know in 10 year usage of calibre there is no way in calibre for loosing a complete library including all sub folders during an installation. You can maybe mess up the metadata.db but never the library itself. The metadata.db can be rebuild easily if needed (as soon as you find your library)
The next question will be something like this: Had you already check/search for a known single book or book file extensions like *.epub, *.azw3 ...? Check as well your AV log. It happen these days more often that a AV is blocking the access to parts of calibre.