I should add the videos are not itunes stored-obtained videos, but those I have collected over the years from all sorts of places and converted to itunes format. Don't know if that has anything to do with it.
I'm using the newest Itunes (version 11) with Win XP. I didn't have this problem with earlier versions on my older computer, but with this version, the thumbnails it grabs from my music videos come up black or distorted on my iphone and on the menu in the itunes program. I assume it's grabbing the thumbnails from the very first split-second of the video. The thumbnails look horrible. On my video menu in MY VIDEOS they look fine. Under the old itunes programs they looked fine. But on my phone and in the NEW itunes program they look black. I haven't been able to find a fix with any research, and I'm hoping someone can help me find a way to fix itunes. Any suggestions on how I can perhaps change the thumbnails to something a second or two into the video instead of at the opening moment of the video?
Now to my second problem... I went to a new install of itunes because of a computer crash to start with, and moved to a back-up computer. This new itunes install does not play videos. They're choppy with no audio. While my emachine is an older model, it is actually a bit better model than my older one which ran version 10 just fine. This one also does online gaming and basic streaming video fine. I have the newest quicktime installed. I have removed and reinstalled itunes several times but I cannot troubleshoot why videos won't play on this program. Can't afford a new computer so if anyone can help with these issues, I can use it!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic