Windows Vista Vista-XP Boot Mess

So this is a bit of a complex problem but I will be as clear as I can.
p.s. I am a complete newbie

I was running Vista Ultimate.
I installed Vista updates from microsoft and got BSOD.
I tried rebooting into safe mode but it would crash and restart the computer before the OS loaded up.
I found an old XP SP1 boot disk from an ancient compaq laptop and thought I would use that to install XP and figure out what went wrong.
The XP setup utility started and I allowed it to copy files into my C:/Windows folder (So I guess it overwrote the old Vista files in that folder)
Then it asked me to restart the computer but I got "Error Loading Operating System "
I rebooted and restarted XP setup and can access th Recovery Console but don't know anything about Recovery Console and what I should look for or do.

I have a Vista Ultimate DVD and tried to boot from there but it still gives me "Error Loading Operating System "

I have a CD with "Active BootDisk" on it but even that doesn't load up. It still gives "Error Loading Operating System "

I read somehwere that I may need to change my BIOS settings but I keep getting prompted for a BIOS password and don't know what it is since this machine has had several previous owners.

I am completely lost now and would appreciate any help I could get.

 

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