[Android Q&A, Help & Troubleshooting] slimon:
Hello – For all people who stuck at ----- Boot failed – Efi hard Drive

Here is a solution that is worked for me – not the same as in the post or comments – but similar

Also this is the fix for people in which drivers is not installed – they stuck at 66% in install

This is My problem so you be aware of the situation I were been in :

I got this Lenovo tab S8 50LC Variant from a friend who was trying to flash it but he went to (Boot failed – Efi hard Drive) – Recovery not working nor fastboot or anything – only fast boot starting … screen by pressing Volume Up + Volume down + Power to boot

So First of all Driver Problem Fix : -

as I saw in comments – a lot of people just install driver thinking it will recognize it alone – but most cases it don't – and if it did recognize in one mode – it is not same driver for other mode for example :

My device was recognized as ADB in fast boot starting

But not recognized in fast boot screen as it is not same driver so to fix it:-

1 -Go to device manger (search Google for how )

2 -Now locate the following each time you change from mode to other is recognized – Lenovo Adb device – not anything else as Samsung … etc.

as the picture follow – if it is like that you are good to go IN THIS MODE ONLY – Check when you go to other mode as fast boot or another

[IMG="Device manger show lenovo adb device"]https://s8.postimg.org/xjvrd0h05/image.png[/IMG]

3 - If it is not - there is ( Android device ) under Unknown – this is your problem not working

4 right click on it – choose update Driver software

5- choose browse my computer Then in choose the folder go to

C:\Program Files (x86)\Lenovo_TAB_S850_Driver

This is where you installed your Driver . make sure to check (include subfolders) .

now it should install your driver – or not ?!

I got this error

system cannot find file specified

so I went to install it manually – so repeat steps until 5

choose – Let me pick from list …

-	Choose show all drivers – until you reach screen which contain button (Have disk )

-	Now go to the same driver folder and install it as before – or not ?!

You might find that it tells you this driver is not signed or The third-party INF does not contain digital signature information - like that – you will need to turn this feature in windows

Useful video on how to do that

search youtube

Fix: The third-party INF does not contain digital signature information - Windows 8

(can't put links yet :D )

then repeat driver installation again

------------------------------------------------------------

Now Back to efi failed problem – how I fixed it

Long version if you are interested : - (short steps in the end ):

What I used is

Phone flash tool 5.8.2.0

Software official :

tabs8-50lc_s139_141010_ww14_bmain_row_us

Repair Bios.zip

S8Unlocker

So according to the method in post – you should boot to fastboot starting … screen (Volume Up + Volume Down + power)

Connect your device and run S8 unlocker – this was not working for me

As I waited for very long time until device was out of charge 

So I run adb devices command and guess what – no devices in adb !! – but in flash tool it was recognized by Dnx – so I put the bios repair in flash tool and flashed it – now I was able to go to fastboot again 

Now in same session in fastboot normal screen – I can run s8 unlocker

After that device don't show Efi boot any more – but it is stuck at Lenovo logo – but now you can go to fastboot normal if you pressed volume down and power when boot

Tried to flash software – after it finished I got efi boot error again

After a lot of tries the same way with different order – no luck

So went to read a lot of comments in this post – some got interested me

Someone saying how the s8 unlocker of bailka011 is working

And he said it is the same esp but with hashtool.efi file added to it

So I couldn't install s8 unlocker after software – as I get efi boot error – and s8 is not working in it

So I have power iso – used it to open the Esp of the firmware – and esp of s8unlocker ( found inside %temp% folder of windows)

Got hashtool.efi from s8 unlocker – inserted in the same place in the firmware – flashed it – WORKED Like charm didn't need to unlock it –

So this how I did it :

1-	Get the following

-phone flash tool latest version

-drivers installed and recognized in device manger

- your software ( I Used tabs8-50lc_s139_141010_ww14_bmain_row_us)

- s8 otkat (for the pft xml file)

- repair_bios.zip

- S8 unlocker tool

-.img files editor – I had power iso – you can use it – or any other alternative

All this tools (except software you can get it from the this post and the Power ISo from the internet )can found in [MENTION=3105136]mac231us[/MENTION] file about how to downgrade to KK (very helpful file)

search thread for mac231us and you will get to it ( can't post links yet :D)

Now how to get rid of EFI error + install your software :

1-install phone flash tool – drivers – and boot device to fastboot starting … sscreen (" Volume Up + Volume Down + Power " when you boot until vibration – release power)

And make sure to install Dnx when prompted in installation of phone flash tool

2-	Open phone flash tool – go to option and uncheck (force fastboot sparsing)

3-	Now extract repair_bios.zip – then open flash tool – browse the flash.xml in repair bios

4-	If it is stuck in the middle make sure when you go to fastboot normal that you are recognized again in device manger – then go back to fast boot starting … again and repeat

5-	Now it should finish with success ( and boot to fastboot normal screen ) – here is the action time :D

Run S8unlocker tool – and wait it to finish – device should boot to lenovo screen no efi error – just stuck at this position - you can go to fastboot normal by powering off – then volume down + power only

6-	Now extract your firmware in a folder

7-	Extract S8 otkat (both files inside) in the same folder and replace file in it

8-	In the extracted firmware folder – locate this file (esp.img) and open it with .img editor (Power ISO – or alternative)

9-	Open run ( press in keyboard windows key + R) and type the following

%temp%

It should open temp folder – inside it there is a folder called afolder

This is the folder created by S8Unlocker tool

Inside it you will find another esp.img – open it in a new window of Power ISO or your program – inside this s8unlocker esp file go to

Efi/boot/

Inside you will find Hashtool.efi

Copy it – then go to esp inside extracted firmware – in the same location (Efi/boot) and paste this file

Save file and close both of them

10-	Now open flash tool – browse to pft_flash_lte_normal.xml file in your firmware extracted folder – boot device to fastboot normal screen – flash it – and it should work like charm

11-	Thanks everyone in this post all of you really helped me with this problem

12-	Sorry for very long comment :D