Check to see that the Via Miniport IDE driver is not installed.
In fact, uninstall the VIA IDE drivers in favor of XP PRO SP2's Microsoft driver.
Next, you can load Via's latest motherboard support package from http://www.viaarena.com as this provides support without replacing Microsoft's more reliable IDE drivers.
Lastly, go to Windows Device Manager and check to see that the secondary IDE controller is operating at UDMA 2. If you see Multi-Word DMA, then that means that you have a bad (or obsolete) cable, or that you need to go into the motherboard BIOS standard section and set the secondary master channel to auto detect with auto type so that it will load full support for the BenQ using UDMA 2.
On the BenQ drive, the green light will go off/become dark if an incompatible disc is inserted. It is also possible that the drive may have a bad flash. Does it exibit this behavior if you use L9 or previous firmware?