If the size of deleted files are too large for the recycle bin you usually get a message saying this and they are deleted without being put into the bin. Is this the case?
You may need to unhide hidden files:-
Start - Control Panel - Appearance and Personalization - Folder Options Click on the View tab Under Advanced Settings click on Show hidden files, folders and drives then click ok
Also in the View tab scroll down and make sure you have unchecked "hide protected operating system files"
Check your recycle bin properties - right click on the icon - Properties make sure that the "Do not move files to the recycle bin" is not checked