[Asus Padfone X and S] ninekaw9:
I had stuck on ASUS logo, after I do a lot of researches, a lot of trials and errors for 4 hours. I managed to fix them and I wanted to share how I did here.

Easiest way to root lollipop WW-12.2.2.27

use KingRoot from http://www.kingroot.net/down ,It is android app which will run exploit to root the device successfully.

Not Kingoroot

Kingoroot was unable to root. Towelroot v1 works only on Kitkat, but not lollipop.

To boot into fastboot mode

adb reboot bootloader

OR turn off device, press and hold power and volume up, until asus logo appear, and stuck at asus logo, that is fastboot mode, to exit fastboot with buttons, press and hold vol down and power button.

To restore stock recovery and ROM after you install TWRP or CWM, or unbrick device

First, note that stock recovery from http://xdaforums.com/showpost.php?p=59055653&postcount=29, does not work for me (maybe everyone else as well).

I flashed it using fastboot flash recovery recovery.img, when I try to boot into recovery using, vol down and power, then select enter recovery, it stucks at asus logo.

First you need to flash TWRP_2.8.7.0.img from http://quarx2k.ru/asus_padfone_s/recovery/

using fastboot flash recovery TWRP_2.8.7.0.img It will show that flashing FAILED (remote: can't flash unsigned image), it fact, it was succeeded, now you can go ahead and boot to recovery.

Note that this version of TWRP, and 2.8.6.0, and CWM cannot successfully flash stock zip ROM, it may show errors, or when you try to boot the device, it will stuck at ASUS logo. But now, we are going to need TWRP_2.8.7.0 to unlock bootloader.

Let's unlock bootloader

simply flash http://quarx2k.ru/asus_padfone_s/CrowLock_RC3.zip with TWRP

You can check bootloader status with fastboot oem device-info

Before unlock :

(bootloader) Device unlocked: false

After unlock

(bootloader) Device unlocked: true

Let's flash stock Kitkat Firmware

You have to unlock bootloader becuase, well it is complicated.

The only TWRP recovery that can successfully flash stock .zip firmware from ASUS is http://datbak.com/links/padfone_s/asus_t00n_twrp_2_7_1_1.img

But this recovery has another bug, if you flash recovery and try to boot to recovery, you will get blank screen, but TWRP is indeed working, you touch the screen and it vibrates back. Anyway you have tofastboot flash recovery asus_t00n_twrp_2_7_1_1.img because it will be needed later for upgrading Kitkat to Lollipop.

If you don't unlock bootloader, you will not be able to boot into recovery directly without flashing to recovery partition Now let's get into fastboot mode, and fastboot boot asus_t00n_twrp_2_7_1_1.img, by booting into this recovery directly via fastboot without flashing it first, you will not get black screen bug of this recovery., if you boot to this recovery from recovery partition, you will get black screen as I told previously.

Now let's flash downgrade to 4.4.2 firmware from http://dlcdnet.asus.com/pub/ASUS/Mobile_Phone/PadFone_S/UL-ASUS_T00N-WW-99.99.99.0-user-wipedata.zip with TWRP 2.7.1.1.

This is for only WW SKU, not TW SKU. And all userdata will be wiped.

Browse all firmwares and there is TW SKU downgrade here : https://www.asus.com/Phone/PadFone_S_PF500KL/HelpDesk_Download/

Ok, now reboot to system, and yeah, it finally boots now.

The recovery is still TWRP, not stock one, let's upgrade to lollipop and restore stock recovery using TWRP. Simply place http://dlcdnet.asus.com/pub/ASUS/Mobile_Phone/PadFone_S/UL-ASUS_T00N-WW-12.2.2.27-user.zip to root of Internal Memory, unplug usb, press confirmation in notification to begin install lollipop. After device reboot, it will stay blank screen for 5 minutes, don't worry, it is updating to lollipop, after upgrade is done, it will reboot, and recovery will be restored to stock recovery now.

Bootloader is still unlocked.

Another method to root is

fastboot flash recovery asus_t00n_twrp_2_7_1_1.img (recovery is restored to stock now remember)

then flash https://download.chainfire.eu/696/SuperSU/UPDATE-SuperSU-v2.46.zip?retrieve_file=1 with TWRP.

To lock bootloader again, boot into fastboot

then fastboot oem reset-dev_info

But I wouldn't recommend you to lock bootloader, you will lose ability to boot to TWRP recovery without replacing stock recovery, unless you are going to send your device to service center and claim warranty.