[Q] Can't Install Supersu On Oneplus One - Stuck On Black Screen! Help topic

I recently decided to root my oneplus one. However i ended up flashing a custom rom (cm12 Lollipop) before flashing the supersu binary. I downloaded the latest version of supersu and copied it onto the root of the phone and flashed it via recovery countless times. But for some reason, after i boot the phone back up and open supersu, it just lags and then displays a black screen. I downloaded it from the playstore as well, but it just won't open. Root checker says its not rooted, despite having a custom rom installed. What do i do?? Please help