This depends on your active directory, if you have another domain controller which is still working, we may be able to restore the servers,
However, if you don't have a backup domain controller in running state, out best shot is to install a new DC and a fresh MS Exchange setup, and re-create users and import old data to the new setup. Provided that the nature of your server crash is hardware caused, and not an infection.
More information needed on the nature of your old setup and the cause of the server crash before I can commit 100% on this.
Note that additional software might be needed for the import of old data to the new Exchange server