I've had that from Lovefilm, DVDs which will play on (some) DVD players but not on the PC. Mind you, I've also had some I could rip to hard disk on PC which wouldn't play on the DVD player or play on PC (so I played it from the hard disk and then deleted it). Sometimes it's the DVD itself (a replacement is fine), other times it seems to be an anti-copying measure.

I can't do streaming things, the net connection is too slow and intermittent.