did you use the Launcher from this page (under downloads at top of screen) to install a new version of the game (its the same game as the one on steam, only the launcher is different) ?
If not -> get the Launcher from the download section here. Place it in a new folder (C:NewStarMade would do) and restart that launcher than from there and let it download a new copie of the game (to be sure in the Launcher : Options-> Installation settings->Path choose the new starmade folder there)
Other people had problems installing the Steam version, data corruption or something like that.
other than that it could be that your system is not capable to run the server and client at the same time (that is basicaly what you do on singleplayer) then you would have to stay with other peoples multiplayer servers
If not -> get the Launcher from the download section here. Place it in a new folder (C:NewStarMade would do) and restart that launcher than from there and let it download a new copie of the game (to be sure in the Launcher : Options-> Installation settings->Path choose the new starmade folder there)
Other people had problems installing the Steam version, data corruption or something like that.
other than that it could be that your system is not capable to run the server and client at the same time (that is basicaly what you do on singleplayer) then you would have to stay with other peoples multiplayer servers