please help my tab 3 lite doesnt install unknown source apps

[sultan]

Hello im sultan.

I dont know why but when i buy it i downloaded master root to root my tablet then enabled unknown sources after that opened downloads tryed to install my app.
What happened that i pressed "install" over and over again it didnt do any thing pressed cancel works

 

[B. Diddy]

Welcome to Android Central! Do you have any screen dimming apps installed? There's an odd Android glitch where if a screen dimming app is active, it can actually grey out the Install button if, for example, you're trying to install an app from Amazon Appstore. Try turning off the screen dimming app, then try again.

 

[Sultan Alofi]

I tried that it doesn't work