First of all, try to edit resolution
And also please check if there is not Webzen MuOnline client on your pc, if yes, then first uninstall Webzen via Control Panel.
After that, redownload MuPlanet and try to run.
To run the game on your computer you may require additional components of the software.
Download Microsoft .NET Framework 4
Download Microsoft Visual C++
1. Set your DEP (Data Execution Prevention) for essential Windows programs and services only
Go under My Computer > System Properties > System Protection > Advanced > Performance > Settings > Data Execution Prevention > Turn on DEP for essential Windows programs and services only
Video Guide: https://www.youtube.com/watch?v=... * Restart your computer
2. Install NET Framework and Visual C++ 2010 Redistributables. Update your PC and its drivers
3. Add MU folder to exceptions list in your Antivirus
Video Guide: AVAST Guide, AVG Guide, Bitdefender Guide, Microsoft Security Essentials Guide
Image Guide: http://imgur.com/a/j0UQx * Turn off bitdefender false-positive alerts
4. Disable Antivirus, Firewall and Windows Defender
Video Guide: https://www.youtube.com/watch?v=...
5. Windows 10 users must install directx9 if your mu client window closes after loading bar
Windows 8/10 users must set main.exe compatibility to XP SP2 or Win 7 and Run as Administrator
Image Guide: http://i.imgur.com/mOaOvRy.png
Download Link: https://www.microsoft.com/en-us/download/details.aspx?id=8109
Contact us at via PM if you have problems with running game after all those steps
Download Video Drivers