I just wiped my mac and just made a fresh install. When I do so I usually install a new version of LR and import my old catalog (that is usually converted properly). This time it everything has gone flawlessly until at the end of the import procedure I can't see any folder or picture I had in my old catalog and can't do anything about it. does anybody have a clue of what's happening? Thank you!
Generally speaking you do not want to "import" your catalog when moving to a new computer with also having a new version of lightroom, but follow a series of steps to ensure everything is preserved including presets, calibration profiles (if used), etc. A good resource is here, but fundamentally you want to find your catalog, photos, presets and templates, and lens/camera profiles (if you created any yourself), and plugins. Move them all to the SAME locations on the new machine. You do not need to move the preview folder. Then install lightroom on the new machine, and open (not import) the old version catalog. Lightroom will automatically convert it to the new version (leaving the old catalog unchanged). Since the photos are in the same place (e.g. drive letter) it should locate them.
If having the photos in the same location is not possible (e.g. you must change drive letters), AFTER you let lightroom convert them, go to the folder display and use the context menu to tell Lightroom where each folder is on the new machine.
Note especially that presets on the old machine could be in two different places depending on your choice for the option to store them beside the library (the above pointer explains).
Once all is stable and you get a good backup delete the old format catalog so as not to be confused later (if you open it again it converts again).
What happened with you likely relates in some fashion to the location of the actual images; it may be possible to use the context menu on the folder display on the new machine to find the location of the top level folder(s) and have them found -- assuming the images actually made it to the new machine, did they? But you should still look into the other things (such as presets and templates) to see if you needed to move them as well. Not everything is saved in the catalog.