Unrecognisable file names in Document Folder

Hello

I have installed Norton 360 in my computer.  Recently I have run the Fix Now program to check if my computer is infected.  The result was "No threat found".  But my Document Folder still is full of file names that do not belong to me.  When I tried to delete them one by one, some of them will not let me delete, instead, i get a ringing (bell) sound.  Could you kindly explain why this happen.  How can I get rid of the unnecessary files? 

Your prompt reply would be greatly appreciated.

Best wishes

Orchid