Corrupted video files

I am having a rather annoying problems with windows 7.. I have spent the last several months ripping my DVD movies to my system so I can use them in windows media center.. I have noticed in windows 7 several of the videos are now corrupt.. The videos will no longer play and a couple of them are now smaller in size then they were originally.. One movie (land before time.. for my kids) I just ripped about an hour ago.. It worked fine then but now will no longer play.. Its not a huge disaster since I own the movies but its worrying me if this problem continues through the rest of the videos.. Thanks in advance for any help you can give..

"Corruption" would imply they won't play on any playback device or software. Is that true? Or are you just having playback issues with a particular application or piece of hardware?

Thanks for the replies.. They will not play in windows media player.. They will play in media player classic but it can play corrupted videos anyway.. The files sizes for some are also reduced.. They also dont seem to be as a result of ripping them in windows 7 as some of the corrupted were ripped months ago others just ripped tonight.. They played fine then all of a sudden they no longer will play.. No thumbnail either.. When I play them in media player classic it will play but the video is not all there.. I am using a bought copy of dvd ripper ultimate.. Dont believe its the ripping program though as I have used several over the last couple months (All trial versions except dvd ripper ultimate)..

Same problem here. Not very happy with Windows 7!!!!!!!!
Have hundreds of downloaded video files, half of which are now corrupt after installing Windows 7. And yes the are corrupt. It is definately an OS problem. Please help rectify this problem before I either go back to XP or buy something else, I am not to happy. Here are some specs.
Sony PCVRS430G
Intell 865PE
Pentium 4 2.8G HT
2G RAM
ATI 4650 HD card (updated driver)
Genuine Windows 7 - 32bit
Win7 codecs installed
The files being corrupted show no sign of continuity. Some are mpg, avi, and wmv. They DO NOT display a thumbnail (as they once did), nor do they play in Windows Media Player (or Center), Real Player or VLC Player. I tried burning a media disk with some playable files and some corrupted pc video files, the files that would play on my pc played in my DVD player, and the corrupted files (on pc) showed up as corrupted in my DVD player. I also tried transfering the said files via USB Flash Drive onto my Sony PS3 with the same results.
Please Help

Just an update for some reason the problem has went away.. I am not longer finding corrupted video files.. Not sure what happened..