For those would like to "root" the ASUS Transformer Prime in Windows, all we need is the ADB driver, but most of the Google results shouldn't help.
After tried How to Install Transformer Prime USB Drivers on Windows! and [ADB/FB/APX Driver] Universal Naked Driver Beta 0.5, Only the Portable Devices - MTP (Media Device) could be recognized.
After all, goto Support For Eee Pad Transformer Prime TF201 -> Utilities -> ASUS Sync V1.0.76, install it. The PC will be rebooted and the yellow Exclamation Mark will go away!
Have fun with the ADB working fine (^^