Problem with Lite-On LDW-851S

Hi - having owned this drive (LDW-851S) for a couple of years, I’ve only just attempted to use the DVD aspect of it, but am getting no joy. It works OK reading CDs, but it will neither write to or read DVD-R, DVD+RW.
It came with Sonic MyDVD software, but not sure if it came with driver disk. I tried installing latest firmware from Lite On site, but still no joy.
In fact, I’d like to go back to the original firmware - anyone know where I can download this from? And are there known issues with this drive and Windows 2000 SP4? Board is Asus A7V133 with Athlon 1.2GHz cpu. Thanks.