You must have installed Zenphoto on your webspace/webserver somehow. You must have some credentials to that webspace. If not your host can tell.
Perhaps you used a 1-click install provided via your host. In that case your host must be able to help, too. Point your host to the first link I posted above. That is the only way to workaround for an forgotten password.
Probably you are on an outdate Zenphoto version as well (you did not tell), otherwise there also should have been a link to request a reset of password via the mail address attached to your user account. But if there is no mail attached it also come down to above instructions.
But if you are indeed being hacked, you should do an reinstall in any case to be sure no files have been hacked. In that case your host should be able to help as well, especially were they did come from.
I am sorry, we cannot help as we are also not involved in your installation.