Super Drive won't read blank media, will read others just fine...

Hi there -

My HL-DT-ST DVD-RW GWA-4165B superdrive on my Power Mac G5 has suddenly stopped reading blank media. When I put it any blank DVD-R or CD-R - of any brand - I get the alert that says "You inserted a blank DVD. Choose an action...etc.". If I choose "open in finder", I then get an alert that "This disc cannot be used because it is not recognized." If I try to ignore the "choose an action" alert, and burn something from the Disk Utility, I'm told "The disk is reserved for exclusive use by another application."

I'm able to run existing DVDs and CDs just fine.

Everything was working fine just last week. The only thing I've done of any significance since then is create a disk image from a DVD, using Disk Utility. But I've done that before without any problems at all.

I've reset PRAM, restored permissions of my boot drive in Disk Utility, and the Super Drive is showing up fine in the System Profiler.

Any ideas???? Any advice or assistance is hugely appreciated!