Or without an OS installed at all, or with a broken OS.

I do VoIP phone systems for a living and this is why I deploy Supermicro mini-ITX servers, so even if something goes totally sideways as long as the client's IT is competent enough to get me remoted in to their voice network in some way I can troubleshoot it fully and in many cases fix it without leaving my desk possibly half way across the country. If it's an actual hardware problem and I can't fix it remotely I still then know for sure what's wrong and whoever's going on site can be properly equipped for the actual problem rather than having to bring everything.