Had to reformat and reinstall everything.

[pocaracas]

So over night, the night before last, my computer suddenly freezes and gives me a blue screen upon reboot asking for "bitlocker recovery key".

Did you ever install some sort of hard drive encrypting software... like bitlocker?
Bitlocker is a legit piece of software that M$ integrated into Windows: https://support.microsoft.com/en-us/wind...1561aae838

Maybe you or someone with admin rights activated that for the boot drive the day before things went awry and forgot to tell you the code?
It's too late, now, but that could have been an option.

Another option is some malicious code activated it for you and then asked you to pay up (possibly in bitcoins) so "they" could give you the code.
If you feel this is what happened to you, my advice is to, from now on, use a better anti-virus than the one shipped with Windows. The Windows one isn't terrible, it's just not that great.
Don't use Norton, that thing is a virus in itself. Use Kaspersky, Avira, Bitdefender... and can't remember any other decent ones (tbh, I haven't looked into the anti-virus market in a while, so there may be newer/better ones around)