Adding a subdomain shouldn't break your SSL, and you don't give your domain so there's no way to see what you've left out. You also don't differentiate between offline now for 24 hrs and ssl broke.
So it's hard to understand what you mean.
Whether reinstalling the cert will resolve the problem depends entirely on what broke, and you don't give enugh information to know that.
To reinstall a cert you must have installed or reinstall the private key as well as the Cert supplied by your Cert vendor, and if necessary, any chain certs they require.
Jeff