You shall find it useful in-case you have rooted your phone or want to refresh the OS or have a different android installed, such as ColorOS/Cyanogenmod/ OxygenOS or any other. In this post, you shall find the step by step process to restore the latest Factory image(Cyngn) to your OnePlus One Phone.
This will allow you to install Cyngn/Cyanogen 12.1 (Android 5.1.1) on your OnePlus One /OPO phone
You may also use this howto to restore any or the image listed on https://cyngn.com/support
To start with
1. Download the factory image
Find the appropriate image for your device
In this case (updated on 8th March 16)
2. Install the adb tools (adb and fastboot).
Alternatively
A simple installer could be for the XDA forum which is a “This is All-in-One installer for 3 most needed PC tools for Android. No need to download big SDK for 3 small things“. The installation steps are also provided on this site, which I followed.
Ensure they are accessible globally. On windows do it by by adding the adb and fastboot binary path (“System properties” -> Advanced -> environment variables -> System Variables -> path) so that both the commands can be executed from any present working directory on the command prompt. For more information on setting the path use this link.
3. Preparing the device for installation (Enable debugging mode on your android device)
the next step would be to enable debugging mode on your android/nexus device
Setting -> about phone -> Build number; Tap on the build number 7 times to enable developer mode, which will enable developer option under setting
Setting -> Developer option -> android debugging; set it to enable and you are ready to work with the adb tools
One the debugging is enabled you can connect the device over usb cable to a USB 2.0 port on your pc. On connection it it will try to install appropriate the driver automatically. in case any of the above steps fails, follow this link for detaild steps How to install adb tools and android device drivers,
use the following command to check if adb tools can communicate with the device
adb devices
4. Extract the factory image
Using your favourite file extraction program to extract the package to your Desktop (I used winrar). *** Remember, if you don’t have adb/fastboot in your Path, extract the image into your adb/fastboot folder **
5. Get into bootloader/Fastboot mode
Use key combination or the following command to get into bootloader
adb reboot-bootloader
or
Enter fastboot mode- Turn the phone off. Hold volume up + power until the “fastboot” screen appears.
Now run
fastboot devices
This command will list the connected devices. If your phones serial number shows up you are good to go and may continue. If the phone is NOT listed this indicates that your drivers are not installed correctly. In order for you to continue you must fix your drivers so that your phone is listed under fastboot devices.
6. Unlock the bootloader
First you need to check the device (OnePlusOne) lock status
fastboot oem device-info
You may get the following output
…
(bootloader) Device tampered: true
(bootloader) Device unlocked: false
(bootloader) Charger screen enabled: false
(bootloader) Display panel:
OKAY [ 0.010s]
(bootloader) Display panel:
OKAY [ 0.010s]
finished. total time: 0.010s
If the phone is locked, proceed to unlock the bootloader with the following command:
Remember that this step will wipe EVERYTHING off the phone
fastboot oem unlock
You may get the following output
…
OKAY [ 0.002s]
OKAY [ 0.002s]
finished. total time: 0.003s
7. Flash the factory image
Once you’ve unlocked the bootloader, and rebooted the phone, turn the phone off and back on into fastboot mode and reconnect it to the PC. You can run the following commands one by one, or create a script which includes the following commands and name it flash-all.bat/flash-all.sh and run it These automate the flashing process. Once complete, the phone will reboot.
fastboot flash modem NON-HLOS.bin fastboot flash sbl1 sbl1.mbn fastboot flash dbi sdi.mbn fastboot flash aboot emmc_appsboot.mbn fastboot flash rpm rpm.mbn fastboot flash tz tz.mbn fastboot flash LOGO logo.bin fastboot flash oppostanvbk static_nvbk.bin fastboot flash recovery recovery.img fastboot flash system system.img fastboot flash boot boot.img fastboot flash cache cache.img
8. Flash the user data image based on the device version
Finally, enter the command to flash the userdata file, which depends on how much storage your OnePlus One has.
Note: You could skip this command as this will delete all data on your OnePlus One.
For instance, if your OnePlus One has 16GB storage, enter this command:
fastboot flash userdata userdata.img
For OnePlus One with 64 GB storage, enter the command:
fastboot flash userdata userdata_64G.img
(both these images should be available under the unziped folder as described on step 4)
9. Reboot
That’s it. Reboot your OnePlus One with following command for the changes to take effect:
fastboot reboot
Your OS will boot for the first time and you have to setup your phone.
Technology Tab 
You saved me, 1000 thanks
After performing these steps (minus the userdata step) my phone is now bricked. It won’t power on, won’t charge, and won’t be recognized by the computer as before.
Some times the device wont start if the battery it completely drained, happens to me. eventually it works. I am not sure what causes it.
phone is constantly resetting and going through “Android is starting..” repeatedly without booting to home screen. Wont show up when using adb devices command. help please…