Startup repair hen attempting to turn it on.....it first displays "Preparing Automatic Repair" and then goes into "Diagnosing your PC" and stays stuck there.

Please note all below options are at your own risk and only applies to ASUS Vivotab TF600T.

Option 1: From within Windows RT:
1. Select PC Settings .. General
2. Scroll down to options - a. Refresh your PC or b. Reinstall Windows (see NOTE below) c. Reset from recovery disk. (see Options 2 & 3 below).

Option 2: If you have a saved recovery disk on an usb pendrive:
1. Shutdown your tablet.
2. Connect the recovery disk to your usb port on the keyboard.
3. Keep the volume down button pressed and power up your tablet.
4. Release the volume down button when the ASUS logo appears.
5. Recovery software on disk will start the recovery process.
6. Follow the prompts and choose your language / keyboard options.
7. Select Troubleshoot .. Advanced Options ..a. Refresh your PC or b. Reinstall Windows
NOTE: Selecting (b) will reset your PC to factory settings (so save all your data) and you'll also have to install all updates again - DO THIS ONLY AS A LAST RESORT!!!

Option 3: If you don't have a saved recovery disk:
1. Refer to below link and download the file vivort.rar (over 3.6 GB). Also read all relevant comments on that forum before you begin.
http://forum.xda-developers.com/showthread.php?t=2165831
2. Insert a blank min. 8 GB usb disk in the PC you saved the file and open an elevated command prompt and enter 'diskpart' and then the below in this order:
a. list disk
b. select disk (no. of your usb drive only or wrong drive will get cleaned)
c. clean
d. create partition primary
e. select partition 1
f. active
g. format fs=fat32
h. assign
i. exit
3. Extract/Copy the files to the root of the USB drive, not in a folder.
4. Follow steps 1 to 7 in Option 2 above.

Hope this helps someone.