You will need to open your registry editor for this one. You can find it by going to start and then search for "regedit"

It depends on what type of file you are trying to delete as to what you should do. Regedit works just like your folders do so go to:

HKEY_CLASSES_ROOT\SystemFileAssociations\.avi\shel lex\PropertyHandler

This example is for avi files, if you were trying to delete mp3 files you would do the same thing but replace avi for mp3.

There will likely be a long number, possible mixed in with some letters, just erase whatever you find where it says "value"

Then close out of regedit and you should be able to delete these files no problem.