Don't know if anyone can help with this. My other half recently copied a bunch of cd's onto her i-phone. If I understand correctly this involved copying the cd's into her i-phone file on the laptop (or maybe online?) then downloading to the phone. Since doing this the cd/dvd player on her laptop will not play dvd's but still plays audio cd's. It all worked perfectly before the i-phone upload/download.
Spent a couple of hours on it last night, tried system restore, changing default media player but got nowhere. Luckily it's still under warranty so I called Comet where we bought it and a very helpful guy told me that the CD/DVD player has two recording heads, one for each function, and it sounded like the DVD head had broken down. He offered to get in touch with the manufacturer and get it collected, repaired and returned. Good service that from a company that often gets bad press.