There are a billion things that can cause this.
No, linux doesn't normally do this, but it can happen with any system.
Odds are, you either have something going on that makes it look as though the machine is frozen, or you got a kernel panic.
If you are in X, the next time this happens, try CTRL+ALT+F1 - and see if it will bring you to a prompt.
If it doesn't, reboot, and check /var/log/messages for entries to try and determine what is wrong.