Won\'t detect Blank DVD R (Sony DRU-840A)

[qanda]This thread is about the Sony DRU-840A. Click here to see full specs[/qanda]I bought sony dvd RW DRU-840A some time ago,in the past i used it was able to both write DVD R and read them,but now when i insert a new DVD R in the DVD rom it won’t recognize them,however it does still read previously written DVD’s and those bought.

I am still able to write CD R.
Both the windows explorer and Nero version 7 donot recognize the blank DVD.

i also am having the same problem,burns dvd+ but not -r, please tell me how to solve this situation please,