A Problem About My Portable WD Hard Disk

hi every body.I have western digital 2.5″ 320 gb portable hard disk.when ı want to copy my files to my portable hard disk gives error.it doesn’t let me to copy files which are greater than 4 GB.it says:remove some files,but 280 gb of harddisk is empty.please help me about this error.
Answer #1
is it formatted as FAT32? IF so go to CMD and type:
convert drive letter: /fs:ntfs
to convert it to NTFS. FAT32 formats dont allow files over 4GB in size
Answer #2
yes it is formated FAT32.But you said CMD.What is it?
Answer #3
ok ok.I found it.thank you very much .