The two most common reasons why the cache rebuild doesn't seem to work are:
- The antivirus is slowing down too much the process, that it seems to be stuck, because it has to scan each and every file GSX searches for when rebuilding the cache. This can be usually fixed by excluding all folders containing sceneries ( both the main simulator folder, and other folders too if they are outside of it ), but if your antivirus is so limited that doesn't allow you to exclude whole folders, it's almost impossible to do it file-by-file.
I strongly suggest to switch to a better antivirus, because the ability to exclude whole folders is a core feature that every antivirus should have. The free Windows Defender included with Windows has it so, you would guess a 3rd party one would have it too. If it doesn't, switch to a better one.
- One of your .BGL files is corrupted, making GSX crash while rebuilding the cache. Some of the most common errors, like a file with 0 length, are detected, but if the file looks complete, but contains garbage ( not legal .BGL ), it's almost sure GSX *will* crash ( Couatl will crash, most likely ) when trying to open it to see if it contains airports.