I have burned around 15-20 DVDs using CDBurnXP over time. All the DVDs were working perfectly, until one day I reinstalled Windows XP on my machine. Now Windows, detects all of them as blank DVD. To be sure that DVDs are alright, I checked them on my neighbour's MACBOOK. MACBOOK recognises all DVDs perfectly and all data is being shown. Why is it being then shown as blank DVD in Windows?
If you installed the proper DVD drive drivers your problem may be with how you finalized the disks. Install the burning program you used and see if that changes anything... even if you forgot to finalize the disks the program should be able to see the contents.