DVD RW Will Not Read Media

LG GSA-H55L Super Multi Security DVD Rewriter with LightScribe™

Problem:
Does not read media of any type.

Windows errors:
Access denied.
Not a valid win32 application.

Details:
Shows in My Computer as "DVD-RAM Drive" until media is inserted. Then it changes to "CD Drive" with either "0 Bytes" listed under Total Size and Free Space, or nothing at all. This is regardless of media inserted. I've tried CD Audio, CD ROM, DVD ROM, DVD Movie (all retail) and the same issue occurs. Media disks are all clean with no scratches or smudges.

What I've Tried:
Uninstalling all optical drives from Device Manager, turn off PC, physically uninstall both drives (I also have an LG CD RW drive, no problems with that one in any case), reboot to confirm no drives present, turn PC off again. Install DVD drive as master alone, turn on to test drive. Same problems.
I've tried with the CDRW as master and DVD as slave, DVD as master and CD as slave, DVD alone as master, DVD alone as cable select. The drive has the DVD specific options in Device Manager (DVD Region, etc).

I have no virtual drive software installed. I have all current updates for operating system. I've done complete malware scans (AVG Professional and Spybot S&D). My BIOS is up-to-date with no problems in any other functions of my system. The CD drive works totally fine, read/write regardless of other drives or whether it is master or slave, so that eliminates the IDE channel or cable as the problem.
I bought this drive a few days ago to replace another one with the exact same problem, a LITE-ON DVDRW LH18A1P.
Since the problem has occured in identical fashion with 2 different drives, of 2 different brands (both DVD writers) I can only assume the problem is with my computer.
I've done extensive searches on the internet trying to find a solution, and keep getting the same "answers" with no positive results (usually that the drivers in XP SP2 are the problem).
I would very much appreciate any help with this issue, as it is VERY annoying, to say the least. I bought Call of Duty 4 (PC-DVD) and can't even install it. I can't watch any of my DVD movies or burn any DVD ROM disks.

My System:
ASUS P4P800-E Deluxe (motherboard)
Intel Pentium 4 3.0Ghz CPU socket 478 (Prescott core)
1.5 GB DDR400 RAM
Microsoft Windows XP Professional SP2 (legal copy)