Hi, just put a dvd in my player and the message "cannot read disc" comes up. it was working fine until then, now nothing plays. any ideas? It is a sony dvp ns30 multi region player, about 4 years old. I have tried turning off/disconecting the unit and several different discs

Make sure the dvd is clean. Use a microfiber cloth (like the ones that come with eye glasses) if that doesn't help, use warm water and a bit of soap, dry with microfiber cloth. If it still doesn't work, make sure the very edge of the disc is smooth. You may need to rub it vigerously to get it smooth, this is also a great place to look for tiny cracks.