Toshiba DVD SD-R5002

I have a huge problem that I didn´t have before. My DVD burner Toshiba does not recognize any DVD-R/-RW. I burned all DVD discs till last week without any problem and now …
When I use CD-R/RW or original DVD then Toshiba reads them immediately. But new DVD-R/-RW discs (Commodore, Verbatim, Princo, Bell …) are not recognized. Even disc which were burned in the past are not readable now. I have already reinstalled Windows XP, too but without result.

Can anybody give me some advice ? Thanks in advance, Ron