pleeeease help !!!!!!!!!

i've downloaded a song i no longer want. i've tried to delete it from my library but it wont let me as it says its either being used by another application or being downloaded to !!!! i've even tried to uninstall the program from my computer and then install limewire from a different source. but when i do my "bitdefender alert" pops up and tells me this same song is trying to access my computer. it does say that it is a "wma" type file where as all the other songs are mp3. what does this mean and how can i delete this song for good