itunes doesn't play video

Hello, I have had this problem for years, and it really stinks that I can't watch any of the stuff i've purchased on iTunes.

Any time I try and watch a video in iTunes (that i purchased through iTunes, it freezes and crashes iTunes. If i try and watch some of these movies or tv shows through Quicktime player stand alone, it will play some of them if not most and all of them, but the video for some reason appears sub standard. I am convinced I will never get this issue resolved, which really stinks because i would probably buy more movies and tv shows through itunes. =(

OK: I did a complete gut uninstall of everything apple from my pc, and a registry clean etc. and then a complete reinstall and it still doesn't work.

I also went into Quicktime settings and changed the 3D acceleration settings as some threads suggest.

So other than those things right there I don't know what to say??? I have a 16 gigs of ram, an i7 processor, and HD radeon GPU... my hardware is not the issue. p.s I also watch movies via cyberlink power dvd etc, so I know I am able to watch video. I am thinking i am missing some type of codec... who knows, I don't or i wouldn't be typing this.

😠