[Asus  Eee Pad Transformer Prime] Hobbesian:
Right -

Unlocking with the APK does not root or in any other way modify or prep the prime for what you're about to do. Depending on your stock ROM revision this is either very easy or a complete pain in the ass, I'll provide both versions:

For Stock ROM ending .15 or earlier -

* DO NOT RUN THE GOO IM.MANAGER FIRST. Follow these steps below.

* Download Sparky's APK to root - it's in the development forum for the TF Prime. Run it. This will get you root access on the system. It's automated and practically idiot proof, just follow the on screen instructions.

* If you're going the Team Win route, once rooted, load up the Goo.im manager, then follow the instructions as per a rooted installation for getting TW Recovery into place. This is pretty painless really and works automatically, approve the Superuser permissions as required. Once the recovery is in, you can reboot into it and then get with the flashy.

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If you're on the Stock ROM ending .21, you're going to have to do what I did. As you're already unlocked using the BLOB files to downgrade -will- result in a hard brick. SO!

* Install ADB and Fastboot onto your system, as well as the universal USB naked driver which you can find on this forum.

* Search for DotTech install ADB and Fastboot - follow this guide, it's probably the easiest way to get a working fastboot and ADB environment up and running.

* Enable USB debugging on the tablet under developer options.

* Set up the universal driver, you'll need to reboot your TF201 and hold the POWER and VOLUME DOWN buttons until you see some text in the top corner. Do NOT press volume up to go into Recovery Image mode or you'll just walk into a dead end.

* Shortly after you'll see three icons, press volume down ONCE and then volume UP once, the USB icon in the middle should be highlighted and you should see text saying "Entering Fastboot Protocol" or similar.

* Plug the USB cable into the tab and the PC, test whether you have a working fastboot install by typing fastboot -i 0x0b05 reboot, if your tablet reboots without you touching it, then you've got working fastboot access. Remove the cable, reboot to fastboot mode as described above.

* Meantime, download openrecovery-twrp-2.1.3-tf201.blob from the team win site, and stuff it in the same directory that you set up Fastboot/ADB, rename it to twrp.blob. Plug your tablet back in and then issue the command fastboot -i 0x0b05 flash recovery twrp.blob , if this goes to plan you'll see a couple of lines of text on the command window which will tell you that it's been successfully flashed in. YOU STILL DO NOT HAVE ROOT THOUGH, SO NO SILLY STUFF

* Finally, download the ROM of your choice, place it in the base /sdcard directory, then reboot the tab and hold POWER and VOLUME DOWN, when you see the text, this time hit VOLUME UP, and you'll be sent into the team win recovery suite, at this point you can wipe and flash the newly prepared ROM as per normal.

* For the first occasion I -strongly- recommend you use Virtuous Prime-S as you can generate a solid backup environment out of it, as well as the fact it's not too departed from Stock, so it's a good way to break yourself in.

Hope this helps.