It is most likely dying of old age: this was a 2005 or 2006 model, and Philips recorders of that era were not known for the longevity of their DVD drives. (DVD recorders in general have an average life expectancy of four to six years before the burner croaks.) You won't be able to get it repaired, as Philips exited the recorder business a few years ago and its partner Funai no longer has stock of spare parts.
Since you have nothing to lose, you could try some simple self-service. Take the cover off the unit and see if the DVD drive has an "open" design (not sealed in a case). If you can see the disc spindle when the tray is out, you could try cleaning it with a swab moistened in alcohol. The spindle and clamp can lose their grip on the DVD after years accumulation of dust, so cleaning may allow blank discs to be recognized again. Also try cleaning dirt off the laser lens with a small blower brush and swab. This is more likely to help if you have a smoker or cat in the home.
If the DVD drive is sealed in a case, about all you can do is try different blank discs. If you are using anything other than Verbatim AZO or JVC-TY, quality control and dye formula can vary enough to confuse an older recorder into suddenly not recognizing certain blanks.