You'd need to give more info for people to help.
What format are the videos etc Maybe they are huge HD vids ?
How do you play them ? DVD, SD, USB, SMB ?
If USB or SD maybe your card/drive doesn't have the best support, if SMB maybe you've got a pc problem. You can cancel this idea out by just trying a different way to launch them EG if you load by HDD, try SMB or SD or DVD. If you do and they still cause problems it's most likely the format of the movies, again you can cancel this out if you have a few movies with differnt encoding/format.
If they play for a while the format and codec must be supported, also if they are playing for a while it surely can't be the cIOS.
I never get problems using SMB but my movies are generally 700mb-1.4gb xvids.
You need to narrow down the problem a bit more.