I am having a similar problem; putting in discs I have played before, having them load for a long time and then the message "Unknown Disc" pops up. I am gonna try the cleaner option and then go from there. I love the site!
peri
unfortunately this is a common issue with DVD players over time. They just wear out. Especially if it is a less-expensive model. Not that theres anything wrong with that. If you pay $50 for a DVD player and get a good 2 years out of it, consider yourself as having gotten your money's worth out of it. Some DVD players may last 10 years, i have an old pioneer one from the late 90's that still works, BUT most DVD players have a shelf life of about 3 years. Some shorter.
Most common breakdown is with the disc rotation mechanism. Just stops working, that's why you get that unknown or blank or No disc error. If you keep getting that error, and cleaning the player doesn't work, and you've tried a variety of discs, then it's most likely time for a new DVD player. If you've gotten your money's worth out of your current one, be glad and look forward to getting a new one!
Lot's of new goodies with DVD players now. You can get recorders, and most new DVD players are now UpConvert. Meaning if you have an HDTV system at home, the DVD player will output in HD format. Most even support HDMI now. If you are looking for longevity in a DVD player, stick to the big name brands, SONY, SAMSUNG, PIONEER, LG, even TOSHIBA. Personally i prefer SONY or SAMSUNG, you will probably pay a little more for them, esp if you want a nice upconvert model for HDTV. That will probably cost you around $100+. But i think it's worth it.
Good Luck!