Encrypted Boot - Bitlocker Factory key - Latitude G5590

Hi everyone
After a BIOS upload my BOOT (probably the OS) has been damaged, so (after a total diagnostics of all devices, just to be sure) I tried to Flash the BIOS and restore BIOS factory settings but nothing chances; when i flashed BIOS. after the diagnostics a message comes out: “No bootable devices were found! Possible causes could be a corrupt OS image or a Boot device is not enabled in BIOS setup"
Using Command Prompt, when I try to access C: it says that I must insert a Bitlocker Key but there's no Bitlocker key saved on my Microsoft Account and Microsoft Support says this key is made by Dell and there's nothing they can do.

I'm quite sure the problem is the OS but I can't remove it because of the Bitlocker Key.
Where can I find it?Is there a way to restore the security settings from BIOS? Can I recover the data before I format it?

Pls help, I can't use it since last week.