how to stop installer exe to run if one installtion has already being done

I created one Installer exe(setup.exe) using NSIS and then

i installed it ,Once it is being installed if i install it

again it creates one more instance .How can i avoid this

i looked in the NSIS help there i got the solution for

avoiding the multiple instances that is working fine .It

does not allows to run multiple installer exe to run at

same time but my problem is my problem once being installed

and if some body double click the setup.exe it installs it

again .How to avoid this

!define InstallDirRegKey 'HKLM "Software\MyApp" InstallDir'

InstallDirRegKey ${InstallDirRegKey}



Function .onInit

  ClearErrors

  ReadRegStr $R0 ${InstallDirRegKey}

  IfErrors +3

    MessageBox MB_OK|MB_ICONSTOP "MyApp is already installed."

    Abort

FunctionEnd



Section -InstallDirRegKey

  WriteRegStr ${InstallDirRegKey} $INSTDIR

SectionEnd

Stu

Re: how to stop installer exe to run if one installtion has already being done

Hi Afrow

Thanks a lot