One of my O.S works fine. The other one crashes without warnning

Please clarify your question

Use the one that works? As Curly said, we need to know what you problem is. Also post some more specifications. What the two operating systems? How are they installed (same hard drive/different partitions, different hard drives, etc)? What type of crashes do you experience with the other OS (BSoDs, locking up, powering down completely, etc)?

More info please :)