[Zenfone 5 Q&A, Help & Troubleshooting] Jagernout:
I got same problem (solved)

I have advice for you according my experience.

My device is T00F/A500CG

I assume you can enter bootloader or recovery mode, your pc installed all needed driver to do command adb sideload.

1. Download official ZenFone 5 firmware from ASUS website. Just go to Google and type keyword "download ZenFone firmware".

2. Download firmware 5.3.3.3 and 5.2.2.2 (apply same SKU according your device). because my device use WW sku, so I downloaded firmware WW_5.3.3.3 and WW_5.2.2.2.

3. Place those firmware inside adb folder in your pc.

4. Go to recovery mode on your ZenFone 5.

5. Connect your ZenFone to pc using USB cable.

6. Select menu "apply update from adb" on recovery mode.

7. Open cmd at your adb folder.

8. Check whether your device connected or not by using command "adb device". Make sure your device listed as attached.

9. Flash your firmware 5.3.3.3 using adb sideload command.

10. At recovery mode, select clear cache and user data (optional).

11. Once again, enter menu "apply update from adb" at recovery mode and flash firmware 5.2.2.2 using adb sideload command.

12. Do clear cache and user data at recovery mode. Then restart your device. Its will take time to load operating system for the first time, so be patient. Once you done, your device will be running on kit Kat.

This is other way. If you still want to use lollipop on your ZenFone 5.

Follow the step above until step 10. Once it done, restart your device (it will take time for the first time). You will be on lollipop because firmware 5.3.3.3 itself based on lollipop. And of you want to use latest update lollipop (firmware 3.24.40.87) don't do adb sideload from firmware 5.3.3.3 or it will be fail at 54% and you need to repeat step above from step 1.

If you want to proceed to firmware 3.24.40.87, do this:

1. Download ZenFone assists (I recommend this tool).

http://xdaforums.com/zenfone-5/development/zenfone-assist-t3401996

2. Place downloaded file in a folder and extract it.

3. Run the *.exe file. (Active internet connection needed for next step).

4. Activate "developer option" on your ZenFone, active USB debuging and then Connect your ZenFone using USB cable to your pc.

5. Click on "root" menu at ZenFone assists. ( application will download some file for first time usage).

6. When it done, click on " I'm on android" and your device will reboot and automatically enter fastboot mode.

7. When your ZenFone at fastboot mode, click on "execute" on ZenFone assists.

8. Done,reboot your device and if there is no super SU app installed, don't worry, your device has been successfully rooted. Check using root checker if you doubt that.

9. Successfully rooted, now use ZenFone assists to unlock your bootloader( use menu "unlock bootloader" at ZenFone assists). The processes will be similar

As process 5-7.

10. Install TWRP using ZenFone assists. Its also similar with process 5-7.

11. Download moded stock firmware 3.24.40.87 from here

drive.google.com/open?id=0B7Py5ad2aHwKMHRsZ1NJM0tfLTQ

(Source thread :http://xdaforums.com/zenfone-5/help/how-to-revert-to-stock-firmware-t3303654)

This firmware is completely same as official firmware from ASUS, only changed in Meta.inf file so make it able to flash through TWRP.

12. Place downloaded firmware in your SD card.

13. Reboot your device to fastboot mode and enter recovery mode.

14. Your official recovery now replaced by TWRP.

15. Just touch "install from zip" menu at TWRP and select storage where you place the firmware. Do the flashing process, be patient and wait until done.

16. When its done, using TWRP wipe your cache and reboot your device. It will take time for first boot, be patient.

To restore your device all into normal (relock bootloader and replace TWRP with original recovery). Do this:

1. Enable developer option on your device then connect it to your pc using USB cable.

2. Open zenfone assists and select menu "relock bootloader". I assume you already familiar with this process.

3. Open downloaded firmware 3.24.40.87 and extract droidboot.img, boot.img, and recovery.img from inside the zip file and place them inside adb folder.

4. Reboot your ZenFone to fastboot mode, open cmd in adb device folder.

5. Flash fastboot using command fastboot flash fastboot fastboot.img

6. Flash recovery using command fastboot flash recovery recovery.img

7. Flash kernel using command fastboot flash boot boot.img

8. Enter recovery mode then wipe cache and user data (optional).

9. Or just reboot your device.

10. Done, enjoy.