Comments I can't delete

I have a website that has some comments that I cannot delete. They were attached to posts that were deleted (the person I am working with wanted to clean up some space so delete some posts). Anyway, she wants to get rid of the comments that were attached to those posts but they don’t have the checkbox beside them to delete them. Nothing happens when I hover over the comments either.

Anyone have this happen to them before?

Thanks

Caley