You should help us a bit more, like explaining the model of handset.
The first think you should do with most phones is pull the battery out, but if your phone doesn't let you do that, it's useless advice. Telling us as much about the phone and the nature of the crash allows us to be a bit more helpful.
Sorry to hear your phone has crashed and is unusable.
As Gorf mentioned there's not much advice we can give at the moment as we don' know much about your equipment. Taking the battery out as Gorf explained is a quick reboot which may resolve temporary issues.
Let us know what phone you have and we can look to see what steps you might take to resolve this.