I faced the same issue couple of days back.
Basically its a hard brick but recoverable. Does the phone vibrate if you keep pressing the power button also did you tried connecting it to the PC(use 2-3 different cables) and see what comes up in the device manager.
If you still have the phone I can help you recover it... You need to give me some phone history though like was the bootloader unlocked, was it rooted, which recovery were you running and which rom/kernal was your phone on. Were you using the CM12 nightly.
Also if its a battery issue then you need to open up the back cover and disconnect and reconnect the battery connector(If you are really sure its the dead battery as you mentioned it was on 20% I am sure it cannot just go down to zero like that).
Just noticed, The thread is old, But guys there is a solution which works... So next time try the below steps if you feel your phone is hard bricked
**************************How to Unbrick a Hard Brick OnePlus One**************************
These instructions are for people with bricked OnePlus One devices. A bricked OPO has nothing but a black screen (nothing ever comes on the screen, not even a boot logo), it might vibrate when a power button is pressed and held for 20 seconds, has no Recovery partition, no adb mode, and no fastboot partition. The device might be detected in Linux and you might be able to even send commands to it. In Windows, the bricked OPO should be detected as QHSUSB_BULK USB. You might have a bricked OPO as a result of flashing a wrong kernel, tinkering with the boot logo or bootloader, or your attempt of unlocking the bootloader went terribly wrong.
Please do not use these directions if your phone is stuck in a bootloop, has a working Recovery, fastboot, or adb.
If based on the above you determine your device is bricked, here's what you will need to do...
1. Download Color.zip from
here
After downloading, unzip the archive on your computer.
2. Next, you need proper Windows drivers. There are architectural differences between Windows XP and Windows7/8, so follow directions that pertain to you. If you're like me you've already tried different drivers, including Qualcomm USB drivers for 9006 and 9008. My best advice is to uninstall the drivers you tried. Go to Device Manager, right click on the bricked USB device (QHSUSB_BULK or Qualcomm HS-USB QDLoader 9008) and go to Properties, click on Driver, then select Uninstall. Check the box to remove driver files, if prompted. Then:
2:
Next, you need proper Windows drivers. There are architectural differences between Windows XP and Windows7/8, so follow directions that pertain to you. If you're like me you've already tried different drivers, including Qualcomm USB drivers for 9006 and 9008. My best advice is to uninstall the drivers you tried. Go to Device Manager, right click on the bricked USB device (QHSUSB_BULK or Qualcomm HS-USB QDLoader 9008) and go to Properties, click on Driver, then select Uninstall. Check the box to remove driver files, if prompted. Then:
2a:
Windows XP users:
You are in luck, driver installation is straightforward. Go to the extracted Color.zip folder and find Driver.iso. Extract Driver.iso. Inside the extracted folder find Setup.exe. Run Setup.exe to install the drivers. The installer is Chinese, but all you need to do is click through the prompts.
2b:
Windows 7 and Windows 8:
These operating systems block unsigned driver installations by default. Follow these steps (thanks @
nag4plfor testing these):
Download and extract these Qualcomm 2012 drivers:
Click here for driverz . Connect your bricked phone and let Windows do its thing.
Now something very essential you need to do here is to execute two commands tol allow you to install unsigned drivers for QHUSB_BULK. Click on Start Menu > Type cmd.exe > Right Click and Run as Administrator.
In the CMD window type in the following commands (hit enter after each):
Code:
bcdedit.exe -set loadoptions DDISABLE_INTEGRITY_CHECKS
Code:
bcdedit.exe -set TESTSIGNING ON
After both the commands should run successfully, restart your computer.
You can now proceed to install unsigned drivers from the file you downloaded. Open Device Manager, you should be seeing ugly yellow warning under other devices for QHUSB_BULK. Right click on the name and select Update Driver Software > Browse my Computer for driver software. For driver software location provide the path where you have extracted Qualcomm 2012 drivers you downloaded and make sure 'Include Subfolders' is checked. Proceed through all the installation prompts ignoring any warnings.
3:
Once you have the drivers straightened out, connect your bricked phone to the computer and start it up by holding VolUp + Power to about 10 seconds, and let the computer do its thing. Don't install drivers if they are not installed by itself. Instead launch Msm8974DownloadTool.exe as Administrator (right click on Msm8974DownloadTool.exe and select "Run as administrator") from the extracted Color.zip archive. It will scan all the COM ports and find the phone. That's the one line that looks different in the list. The list is just a list of your com ports and devices. If you unplug the phone and move it to another port, it will show your bricked phone on a different line.
Clicking on "Enum" just rescans the busses. Clicking the big square button in upper right corner scans the phone and reports what's good and what's not. It takes a minute for the scan to finish.
If you don't see your phone in the list of com devices, try unplugging/plugging in your phone a couple times, and rebooting it with VolUP + Power (hold 10 seconds). You will see it in Device Manager as well.
Once you see the phone in the list, click Start. You should see the programs start writing different files to the phone. Each time it writes a file you'll see a progress bar. Once you see this process happening, smile, you know you will be good to go... After all files are written, the com line with your device will turn green. You're good, unplug and reboot your phone. It will boot to ColorOS, the Chinese OS that comes on OPO.
4:
Optional Steps:
Your phone is no longer bricked. You now have a few options to get back to stock. The easiest way is to use a toolkit from
here, or you can flash an image manually by following directions from
here. Download the proper image zip and after extracting it, run the following commands in fastboot mode:
Code:
fastboot flash boot boot.img
fastboot flash userdata userdata.img
fastboot flash system system.img
fastboot flash recovery recovery.img
fastboot flash cache cache.img
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
That's about it. I think if people are still having problems then it's likely due to drivers, or Windows 7/8 issue.
**************************End***************************
It took 4+ hours to find this solution and it took me another 4 to implement it but phone is back to life and is working perfectly.
I just found this solution searching all over XDA and OnePlus forums and
this is the original link to the page.
please keep us updated once you get the new phone.