Looking for help after trying everything I can find in my head and online.  Any advice would be gratefully received, thank you.

Dell tower 5810 running Win 11 very well with no problem until last week.

I was copying over large music files (60Gb) and the transfer stopped - completely frozen.

After leaving things for a while to see if they would sort themselves out (they didnt), I switched off and rebooted.

I can't reboot from the SDD.  The Dell logo appears then nothing under it showing any boot progress.  Rebooting using F2 or F12 show the F2/F12 menus but then freeze.  So all attempts to boot from SDD or to BIOS options do not work.

Other boot options (USB and DVD boot) get as far as "repair computer" then seem to revert to rebooting the SDD OS so go nowhere.

I have run cmd from a working laptop and run repairs on the SDD but can find nothing wrong.

Crucial disk review software says there is nothing wrong with the SDD.

Trying to repair the SDD from any other route doesn't seem to work.

If I connect the SDD to my laptop then try and boot from it via S12 I get error "Operating system loader signature not found in secureboot database ('db')"

I am not at all qualified to comment, my GUESS is its a Win 11 boot issue.

I am able to edit the SDD and replace folders so if I could replace boot folders with those working from a fully working Win 11 HDD would that work ?  And if so, what would that entail ?

I'm looking for any advice at all which may help, thank you.

Regards

David