Before you can start installing new custom ROMs or doing things to your Transformer Prime out of ordinary, I HIGHLY ADVISE you to make at least one backup of your current ROM.
Backing up a whole ROM pretty much backups up EVERYTHING including your apps, settings, ROM, and kernel except the contents of your internal storage.
Step 1. First, hold down Volume Down and Power button together for about 10 seconds until you see the white letters appear at the top left of your screen. When you see that, immediately let go of both buttons and press Volume Up button to Clockwor