Some things that may cause this:
You haven't deleted LM correctly, and a file remains in your appdata.
Your filelog is broken in the installation.
Your antivirus is blocking LM from starting, look
InstructionsYou've missed a file or haven't installed LM correctly, try to install everything from the downloads page again.
-
Please post your update.log below so I can help you with the error that's causing the download box to close.
The update.log file is in your Last Moon folder. You can find it by right clicking your Last Moon icon, and then clicking "open file location" until then, I cannot help you further.