[madis121]

I'm not exactly sure what caused the bootlooping of my Cubot Power, it might have been either a firmware update or installing Greenify on a non-rooted phone.

When I connect my phone to my PC, it picks up the device under device manager, but after a couple of seconds it disconnects and then it keeps repeating like that. Phone's screen remains black and it does not let me boot into recovery.

I've gone through a lot of guides (GetDroidTips, GizRom) trying to install a clean stock ROM on my phone using SP Flash Tool. All of my attemps have failed as SP Flash Tool gives me either one of these errors - "STATUS_DA_HASH_MISMATCH" or "STATUS_DA_SELECTION_ERR".

I've tried different versions of stock ROM, but all of them give the same error. Using different SP Flash Tool versions give different errors - v5.1804 and v5.1904 end with "STATUS_DA_HASH_MISMATCH and v5.1652 ends with "STATUS_DA_SELECTION_ERR". I've also tried using different download-agents that the Flash Tool has, but the error remains. I've also tried flashing just the preloader, but it gives me the same error.

Recently I stumbled upon one of your tutorials on YouTube "How to format a single partition in Mediatek using SP Flash tool", but I haven't tried doing that yet, as I'm not sure whether I might make things worse. Might the tutorial help me with my issue or should I not bother trying it? Or perhaps someone might have other suggestions?

[X3non]

I'm not exactly sure what caused the bootlooping of my Cubot Power, it might have been either a firmware update or installing Greenify on a non-rooted phone.
...
but I haven't tried doing that yet, as I'm not sure whether I might make things worse. Might the tutorial help me with my issue or should I not bother trying it? Or perhaps someone might have other suggestions?

your device has secure boot, you'll need a custom DA to perform read / write operations
have you tried doing a factory reset in recovery mode?
and do you remember the build number of your phone?
lastly, did you try this SP flash (or the DA files within) from cubot @ https://mega.nz/#!gZM3SKpR!j4fyfG1QyyY1s...v2oyYvumTI ?

[madis121]

I'm not exactly sure what caused the bootlooping of my Cubot Power, it might have been either a firmware update or installing Greenify on a non-rooted phone.
...
but I haven't tried doing that yet, as I'm not sure whether I might make things worse. Might the tutorial help me with my issue or should I not bother trying it? Or perhaps someone might have other suggestions?

your device has secure boot, you'll need a custom DA to perform read / write operations
have you tried doing a factory reset in recovery mode?
and do you remember the build number of your phone?
lastly, did you try this SP flash (or the DA files within) from cubot @ https://mega.nz/#!gZM3SKpR!j4fyfG1QyyY1s...v2oyYvumTI ?

Yes, I have tried that version of flash tool before, but just to be sure I downloaded it and tried it again - the same "STATUS_DA_HASH_MISMATCH".
I can't boot into recovery mode, the phone doesn't react (I'm not a 100% sure, since the phone doesn't vibrate when it boots by default) to any of the volume or power commands unless it's connected to my PC. 
Sadly I do not remember the build number, however I know that it was the last update Cubot released for Power. I downloaded it over phone update, but Cubot has made a thread for it on their forum.
What do I need to make a custom DA, if that's even possible? If you have any ideas or suggestions, let me know.

[hovatek]

Yes, I have tried that version of flash tool before, but just to be sure I downloaded it and tried it again - the same "STATUS_DA_HASH_MISMATCH".
I can't boot into recovery mode, the phone doesn't react (I'm not a 100% sure, since the phone doesn't vibrate when it boots by default) to any of the volume or power commands unless it's connected to my PC. 
Sadly I do not remember the build number, however I know that it was the last update Cubot released for Power. I downloaded it over phone update, but Cubot has made a thread for it on their forum.
What do I need to make a custom DA, if that's even possible? If you have any ideas or suggestions, let me know.

You'll usually find the DA in the factory firmware. Attach a full screenshot of the contents of the firmware.

[madis121]

I'm not exactly sure what caused the bootlooping of my Cubot Power, it might have been either a firmware update or installing Greenify on a non-rooted phone.
...
but I haven't tried doing that yet, as I'm not sure whether I might make things worse. Might the tutorial help me with my issue or should I not bother trying it? Or perhaps someone might have other suggestions?

your device has secure boot, you'll need a custom DA to perform read / write operations
have you tried doing a factory reset in recovery mode?
and do you remember the build number of your phone?
lastly, did you try this SP flash (or the DA files within) from cubot @ https://mega.nz/#!gZM3SKpR!j4fyfG1QyyY1s...v2oyYvumTI ?

Yes, I have tried that version of flash tool before, but just to be sure I downloaded it and tried it again - the same "STATUS_DA_HASH_MISMATCH".
I can't boot into recovery mode, the phone doesn't react (I'm not a 100% sure, since the phone doesn't vibrate when it boots by default) to any of the volume or power commands unless it's connected to my PC. 
Sadly I do not remember the build number, however I know that it was the last update Cubot released for Power. I downloaded it over phone update, but Cubot has made a thread for it on their forum.
What do I need to make a custom DA, if that's even possible? If you have any ideas or suggestions, let me know.

I took 2 screenshots of different version firmwares, however I did not notice anything that resembles DA/Download-Agent. If you need any more information, let me know.

[X3non]

I took 2 screenshots of different version firmwares, however I did not notice anything that resembles DA/Download-Agent. If you need any more information, let me know.

what's that 't758_cq_8071c_cubot_pcba' file? can you open the file in hex editor and screenshot ONLY the header
also in that spft version you just downloaded, did you try the other DA files within? 
they're usually named like this DA_PL, DA_*

[madis121]

I took 2 screenshots of different version firmwares, however I did not notice anything that resembles DA/Download-Agent. If you need any more information, let me know.

what's that 't758_cq_8071c_cubot_pcba' file? can you open the file in hex editor and screenshot ONLY the header
also in that spft version you just downloaded, did you try the other DA files within? 
they're usually named like this DA_PL, DA_*

I attached a screenshot of the "t758_cq_8071c_cubot_pcba_63_o1_0_50000_20180413.bin" file. However, it is only 10 KBs, so I don't think that's it.
Yes, I tried all of the DA files: 

• MTK_AllInOne_DA, DA_PL, DA_PL_CRYPTO20 - "STATUS_DA_HASH_MISMATCH.
  
• DA_SWSEC, DA_SWSEC_CRYPTO20 - "STATUS_DA_SELECTION_ERR".