Only playing some dvd and not others

try to clean with a special lens cleaner.

I can't answer the first part of the question, but the DVD going blocky and jumping sounds like fingermarks or muck on the disc. It could be that when you handle the DVD your finger leaves a mark near the outside edge of the DVD. In future wipe the DVD with a glasses cloth, then handle by the very edge only.

I recomend that you clean the lens to see if that makes a difference.
Also you might want to look at my Tip on dealing with DVD's that jump.

clean lens. Laser lens dirty, use a cleaner cd/Dvd set, find on electronics stores or professional Audio/video stores

Have you examined the DVD's to see if they are abused and/or damaged by those who rented them? If there is no damage (unlikely for rental DVD's) what does the 'problem' look like?

All you need to do is set the unit to play back DVDs at 480P instead of auto. That's what I did and the problem has gone away.

you have other programs/tasks running in the background that is interfering with the sound quality.

I would remove things out of your startup and system tray

Does the disc still play in other dvd player? My ILO has always been picky to play rentals so I just have a cheap COBY player hooked up to front inputs of my ILO. I use it to watch the dvds, only use the Ilo to record. Saves wear and tear on my ILO but cannot find a universal remote to operate them both and my tv. If it still records okay thats what I would do, just watch the discs in a secondary unit. Sounds like time to start shopping for new recorder.

Hmmm...not sure but sounds like the vibration from the loud sound is causing the disk to jump. Not sure why that would power it off, but I think your thought to junk it sounds reasonable.

Me three, same thing, reads 'no disc' or just won't play it. I have found that it happens more frequently on rental DVD's and that running a cleaner cd through several times helps but eventually that will even stop working. No idea what the problem is