Big Mini Trouble with DVD and Front Row

Question

Set-Up
I am trying to use my mac mini as a media centre connected to a 42" sharp aquos 1080HD, for sound i use a 5.1 bose speaker set-up, which is irrelevant to my problem, but the mac interfaces with a yamaha rxv661B 7.1 channel digital home theatre receiver, via DVI to HDMI and sound through head phone to RCA set-up that will soon be upgraded to optical. All connected to the appropriate DVD channels on the recevier, video goes to the TV via HDMI. My set-up has no DVD player other than the super drive on the mac mini, the only other input is a Bell ExpressVu 9200 PVR.
My Problem
1. Playing DVDs the brightness on the picture fluctuates in a very regular wave like pulse. What am I doing wrong?
2. Front Row Crashes the computer whenever I try to access any of the movie files. The files play fine when accessed directly or through itunes but crash the system in front row. DVDs play, and the online movie clips play, and music and picture content are no problem.
Any help would be much appreciated
As an aside does anyone know if youtube will be available to non Apple-TV front row users, as well?
Mini 1.83   Mac OS X (10.4.7)   12" Powerbook G4

Answer 1

Everything is plugged into a three pronged plug using a relatively sophisticated surge protecting power bar, but you may be on to something, the power bar has a light to indicate if it is properly grounded and that has not lit up since its been in use, perhaps the outlet isn't properly grounded, I live in a recently renovated 100yr old home.
As for the files they are a mixture of mpg, mov and a number of m4v (that might be my postal not a file format) I mean the ipod format, a lot of the video files I produce I put directly into the ipod ready format.