I Installed Prestashop on a subdomain and now it says: ERR_EMPTY_RESPONSE

I Installed Prestashop on a subdomain and now it says: ERR_EMPTY_RESPONSE.
Also have many problems with other CMSs.

If it happens with all CMS, I suspect that your domain has not fully propagated yet. However, I don’t know for sure without knowing which subdomain you’re actually referring to.