installation - QGIS 2.18 "The program can't start because qgis_app.dll is missing from your computer"

I installed QGIS 2.18 after i had uninstalled the version 2.16. It installed quite well but it is not starting at all. I went into the program directory and click on the exe file and got the error "The program can't start because qgis_app.dll is missing from your computer. Try reinstalling the program to fix this problem". I have installed severally and the same error keeps coming on. Any help?