What PS version were you on when it was freezing?
It may be a scratch disk issue where the scratch disk was full. If it happens again check the available disk space on the scratch disk before closing Photoshop. After Photoshop closes the space opens back up so you have to check before closing to see if that was the issue.
Photoshop can use a tremendous amount of scratch disk so that is my first guess.
Damon Bell
