Not sure when it happened, because I don't play DVDs often, but last time I played a DVD, I slid the bastard in the drive and PowerDVD popped up like it was supposed to--Yesterday and today, though, it opened an explorer window.
I went into the AutoPlay tab of my DVD drive and set every value (I.e., music files, video files) to "Prompt me each time", and the goddamn thing still just opened an explorer window. Then I went and set every value to "take no action", so that in absolutely no circumstance should it ever open an explorer window...and it opened an explorer window.
I deleted and reinstalled PowerDVD. Still only get an explorer window. Micros~1, in their typical helpful way, suggested using System Restore to set my system settings way back to when DVDs did work.
IIRC, there was an option for DVD-video in the AutoPlay tab last time, but the bugger's gone now