If you are having ANY problems and have a 'backup' DVD you need to replace it with an original to see if the problems still exist. The Mk IV is VERY fussy about what DVD's it will read and which it won't. I have one PC where the MK IV will only read a disk that is burnt at 16x, any slower and it won't work. On another PC with the same DVD blanks it will only work when burnt at 4x. I've never had a problem with the DVD's burnt at 4x, but the 16x ones are a bit erratic ocasionally.