Updated my Inspiron 15-3567 laptop on Sunday, and my laptop was working perfectly fine until this morning. I opened it and on the screen was an error and that there was an issue and such with the hardware. Then said I had to do a check up or scan on the laptop to find the issue and resolve it. 10-30 minutes later the issue is resolved and I had to restart my laptop. After restarting my laptop the support assist screen is still there. This time saying, "Operating system Loader has no signature. Incompatible with SecureBoot. All bootable devices failed Secure Boot verification". The only button on the screen is Shutdown, and I've clicked it many times but the screen is still there. Is there any way to resolve this?
Please check outsolution in the link below, hopefully it will be a help to you.
Re: operating system loader signature not found in SecureBoot database ('db'). All bootable devices failed Secure Boot verification
If your operating system is failing the Secure Boot verification, then its boot loader has either been corrupted or maliciously altered. You can try going into your BIOS setup (press F2 repeatedly immediately after powering on the system) and disabling Secure Boot to see if that allows your system to start, but if it does, then it means your boot loader is compromised, and obviously I wouldn't recommend using a system that has been compromised. If it doesn't boot even with Secure Boot disabled, something else has gone wrong.
So whether it's corruption or malice, you'll need to recover from a previous backup or System Restore point if you have one available, otherwise you'll need to either restore from a Dell factory image or perform a clean install of Windows using an installer you would create by downloading the necessary files from Microsoft on another PC. There are some tools that would allow you to create a bootable USB stick that will allow you to copy your data onto another a flash drive or USB hard drive before wiping your system even if your internal drive won't actually boot, but hopefully you have at least a recent data backup even if you don't have a full system backup to recover from. And if you don't, then going forward you may want to consider at least periodically capturing system image backups so that you can restore your whole system after incidents like this. Macrium Reflect Free is a popular option, and as the name suggests, it's free. If you end up using it as a primary backup solution, you may be interested in the paid features, but even the free version does enough to cover periodic images captures so that you always have a relatively recent "known good state" you can roll back to.
bro i also had the same problem but i tried it by my own method
when you turn on press F12 as the moment you see dell symbol
Then i dont rember the exact but select last option below bios setup
then after reaching there ther will be futhur two option you try both one at a time while doing this you will see dell warning to change that setting but you do that .It worked for i too search the whole internet but didnt found the solution anywhere but this my method worked for me hope it will work for you