My Sony RDR - GX210 DVD Recorder ejects the disk?

My Recorder is about 7 months old, and has been working perfectly until this week. I place a disc on the tray and press close. It closes OK and " Loading " shows on the screen. Loading then disappears and the disc tray opens immediately.
Have tried several discs that I have been using , and also tried a brand new disc. all for the same result. I have gone through the " Initial Set Up " process twice, but the problem still exists. Any ideas ?