comments-post.php and wp-pass.php problem

When entering a comment or password the comments-post.php/wp-pass.php come up blank. I don’t know what I could have done. I have changed themes a few times, but it appears to be a problem with any theme I choose to use. Any suggestions on how to fix? (There seems to be a conflict with the CG-Amazon Plugin) I posted under that topic so I guess this one should be deleted?