RAID 5 "OFFLINE" - please help

Hi!

My PE 2900 server  somehow lost power when I was at work a few days ago.
And I have not been able to boot into the OS (Debian 11) since.

I have understood that I can not boot due to that something has happened to the RAID configuration in some way. (Not sure what though.)
But from what I can see, there are three disks that are "missing" and one disk is "ready".

Unfortunately I do not know much about RAID / PERC and I really need your support.

Tried to run DSET (following an online advice) from a Debian Live CD, but I did not succeed.
Also tried booting with "Dell OMSA Live CD" but there were not many options for me to do there, (which I was comfortable with). I have no backup of the disks, so I MUST get this fixed somehow.

I am on sick leave after a stroke and can not afford to leave the disks to a company for help with backups etc.

I really need all the help I can get and even though I have a bad finances, I can pay around $ 50 to the person who helps me get the server back up, or so that I can take a full backup of everything.