On my PC the files in blue are hidden and compressed ones like the uninstall progs for downloaded windows upgrades, but I usually delete them anyway when the download hasn't crashed my PC after a few days.
Are you the only user...............because if not, other users will also have a load of temp files, internet temp files etc.
And if you have a lot of graphics or music, that fairly eats up space.
Why not archive old my document stuff to your other hard drive.
Bookmarks