White Flash issue

Hello everyone,
it is my first time to work n UDK engine and im on iMac, when i use anything inside like rotate, move , etc, the screen is blank with white each move i make
any advice how to fix this please ?

Thanks

Are you using UDK or UE4?
Also, what are the hardware specs of your iMac? Macs very often do not meet the minimum hardware requirement

Hello,
im using below iMac :
iMac (21.5-inch, Late 2012)
processor 2.9 GHz Intel Core i5
memory 8 GB 1600 MHz DDR3

and i mean the Unreal Engine 4.7.6