Deep C
I had similar problems a couple of years ago on a lower spec machine than yours, and whatever I tried it just couldn't seem to cope.
Someone recommended trying a player that used very little processing power or resources and it actually worked !
I eventually did a format & fresh XP installation to clear all the rubbish away and was able to use whatever player I wanted. However, if you just want something to enable you to watch your movies with subtitles etc. until you resolve your problem then try it out...........it's free. It's called BSplayer and supports most formats.
BSplayer