Disk memory full but can't move anything to trash

[Dazdrogheda]

My 50GB memory is unexpectedly showing full on my Macbook Pro but when I go to move anything to Trash it's not registering it at all i.e. when I open Trash it is empty and when I press empty, nothing is happening. I have just spent an hour trying to cull my Itunes folder only to find that it isn't registering any changes because the disk is full. Also Spotlight has disappeared from top corner of the screen. Is this all related?
Mystified

 

[BlueRevolution]

Depending on the formatting of the drive, I believe that files may be deleted immediately rather than being placed in the trash. Is the free space on the disk increasing?