iPod and iTunes not playing many mp3's since recent versions

Many mp3's will not play in iTunes or in my iPod, but they used to before the recent versions of iTunes ame out. These same mp3 files play fine in Windows Media Player, just not iTunes. The files are listed in iTunes/iPod, just simply will not play when you click the play button (nothing happens at all). When I click "get info" on these files, the summary tab is missing information that is listed for the mp3's that still play correctly. The missing info is all in the column on the right (Format, Channels, ID3 Tag, Encoded with). According to the forums, many others are having the same problem. Please help. Thanks.