Firewire and IDE Burners Suddenly Burn Coasters?? HELP!

Hi, Gang:

Weird problem....

I have an XP Home machine that has a NEC 3540A internal DVD recorder
drive and an Aopen internal IDE DVD burner drive paired with a Lite-On
DVD reader (IDE).

I've burned tons of DVDs and CDs on each drive for weeks/months with no
problems....

Last night, however, and out of the blue, my XP machine suddenly
decided it had to be "reactivated." My COA is stuck to this PCs
monitor, which I've lent to my daughter. I haven't driven across town
to fetch it, and I've put off the reactivation (three days left).

Now, all of a sudden, both burners are spitting out coasters...same
media...same software, etc... The disks are verified okay by Nero 6
just after they've been recorded...but they can't be read by any DVD
drive (reader or burner) on any of my PCs.

Reinstalled Nero...but no change.

Could this be related to whatever prompted the sudden need for
reactivation?

WTF? HELP! Ideas?

--KK in MN