1. Une instance de serveur Starmade est déjà lancé sur le port 4242. Something uses that port.
2. IDK why you like using a resident program using up resources through which to download and install your games. My advice would be to permanently dump the Steam software and get your games by simple download from the producer or by torrents. But do as you wish... SM can be downloaded here
StarMade without Steam. Just to make sure your problem is with SM and not Steam.
3. Out of topic: Every little program uses a little more of your resources (computing power) and your total resources are always limited. (You can be a Rockefeller, own a supercomputer just for your fun, still if you install enough crap that supercomputer will sooner or later get filled and unresponsive.) So, to preserve computing power for the games and for whatever you actually need to do with your computer, NEVER INSTALL something you are not sure you will use and find pleasure in its use. What is not already cracked is worthless, believe me. So, why do you need Steam? To get discounts for the games that never worth 10 minutes spent cracking them in the first place?
Please, remember to ask yourself before you install anything:
Do I really need this software? Is there no way I can go on without it? Especially if it's about some piece of software that does nothing by itself, it's just an interface to what you need, but it updates daily, stays always on in your system's memory, needs a lot of resources and has its main purpose to police you (see what software you used, what you paid for and what you did not, prevent you from cracking or using cracked software).
