This problem can often be resolved by performing a hard reset. You can perform a hard reset by holding the power button and the home button down at the same time from anywhere between 45 seconds and a minute and a half. The white screen should disappear and a black screen will appear with the apple icon displayed. After this, the phone will restart itself like normal. What the white screen is signifying is that the phone simply hasn't read the new hardware that you installed in the phone. A hard reset calibrates the device so all the connections are working together and the phone is functioning with the new hardware.
Another possible cause of a white screen is the LCD flex cable becoming unseated from the logic board. The LCD flex cable on an iPod screen assembly is very short. As a result, it can become slightly unseated from its port on the logic board when setting the screen down onto the frame. This is enough to cause display issues, such as a white screen. Fixing this problem may be as simple as putting forth a few extra attempts at getting that LCD flex cable to remain seated in the logic board.
If these suggestions do not work, please feel free to contact Customer Support by phone (1-877-700-0349 Ext. 0) or email (support@iCracked.com) for further assistance.