I don't know understand or what to do with the screen shown,
it says the problem might be:
1. The program is also running under a different user account
2. Media Center 21 and Media Server are both in Windows Startup. You must remove one
3 The program is not responding for an uknown reason.
Please help me!
Sometimes this message comes up when you exit/close MC and then try to restart it too quickly (too soon after closing). Because when MC closes it does some "behind the scenes" processes/procedures, so it is technically still running when you try to restart it. If you wait 60 seconds or so, then restart MC you won't get this message.
MC may not be crashing - it may just be unresponsive. On a new installation, as you are importing your media files, MC goes through and creates thumbnails and analyses audio and does other stuff, so sometimes there is a lot going on behind the scenes.
Also during the analyzing process, if you have a "bad file", that can cause MC to not respond. So if you having problems, you might want to try setting everything up without any audio analysis (go to "Tools>Options>Library & Folder" then uncheck the box "Run auto import in background", and under "Configure Auto Import" uncheck the boxes for "analyze" and "build thumbnails". If either of those step helps, then recheck them one at time until you find which one causes the crash (or unresponsiveness).