To tell you the truth, i have a hard time following your posts...

I wasn't around in 2009-2010, so i have no idear what format your private key has.

• WIF: 51 characters base58, starts with a '5'
• WIF Compressed: 52 characters base58, starts with a 'K' or 'L'
• Hexadecimal: 64 characters [0-9A-F]
• Base64: 44 characters
• ...

At any rate, you should be able to convert your private key into WIF if you tell us which format it currently has. As soon as you converted it into WIF, you should be able to use electrum and follow the wizard to create a new wallet using an existing key... You can do the same with core, but it requires an extra parameter to create a non-HD wallet.

That being said, if you stopped mining around 2010, the total number of bitcoins in circulation would have been little over 7 million. Many of those are attributed to satoshi and other known figures in the bitcoin world. If you say you have an address that was funded with millions of BTC, i don't really believe this... Sorry...

EDIT: fixed a typo: 7 million instead of 5 million...