Dvd works cd-rw doesn't?

hi- a question-
i have a combo dvd +cd-rw.
it reads dvd’s + cds, however it has suddenly stopped recognizing the blank cds i have always used when i try to burn (the cds work on my external dvd burner)
wha can be the problem?

Try using the drive on another system, i mean physically remove it from your system and put it in another and try and see if you have any results then get back. Sometimes system configurations / software or hardware can cause problems like this.