The last time I came across this problem it was related to media format. A friend was having problems like this, tried a few things then tried a + disc, as he was using -, and it worked. Do you know if your lap tops drive will only recogniise one format?
Do the discs still work in the PC? If not there could be a problem with the disc itself.
Have you tried other media types? My NEC 2500A will not recognise platinums for burning or reading, so maybe your laptops drive just doesn't recognise them.