These sorts of problems are almost always to do with too much burning/playing software installed, particularly the ones that autorun when you insert DVD-Video or a blank disc.
The fact that you can burn a slideshow (and not video) almost certainly indicates that there's some kind of software conflict at play - what's Nero supposed to do when some other program (ie. running in the background as a Service) is issuing ATAPI/SCSI commands to the drive through ASPI while Nero's in the middle of burning a disc with its own proprietary ASPI layer? The two ASPI's are probably unaware of the others' activity, and the drive is trying to respond to both.
I bet if you uninstalled all that other crap - like was suggested above - and left just Nero, Plextools, and a player like WinDVD or PowerDVD, your 716 would be just fine.
Get it working, then try other apps after that. If they cause new problems, you get rid of them.