|Richard kind of has it right. Combination drives have two lasers. However the wavelength of the laser light is different for CD media and DVD media. Because DVD media can hold more data the pits burned are smaller. This requires a laser with a shorter wavelength. The laser used for CD media does both the reading and writing. The same is true for DVD media. The power is modulated to fit the task.|
All that said there are some common causes for optical burners to not work as intended. First of all, as Richard stated, they wear out. It takes a more powerful laser beam to burn a disk than to read one. The laser can weaken over time or the lens can become dirty, which can have the same affect of not allowing a full intensity beam to reach the disk.
In your case you state that Windows doesn't recognize the drive anymore. Do you mean that the device is not listed properly in My Computer and Device Manager?
If so, watch the POST screens at start up to verify the BIOS is properly configuring the drive by model number. If that is happening but the drive is wrong in Windows then I suggest you remove the drive listing in Device Manager and reboot.
You need to describe in more detail what the drive is currently capable of doing and what it isn't. Also list all burning programs you have installed currently and in the past.