Disk cache

Without any actual info about your volumes and folders we can't really tell you much. the simple truth likely is that your OS X is still reserving/ restricting mass amounts of storage because while you may have deleted the obvious files, you may still have tons of underlying file version info and restore data. You need to check those things in the file/ folder info panel. Similarly, of course mundane stuff like permissions issues could be at play here. Anyway, you may want to start by firing up your disk utility to even get an idea of the actual disk layout and avialable space(s).

Mylenium