I believe I have a legacy private key but cannot find out how to use it

[Abedabed]

I found a key which begins with a 1 on my old computer (2013) in a text document  and I have been unable to work out the process from here to get to the bitcoin if it exists.

I have downloaded Electrum and in the import Bitcoin Addresses menu typing my key in does not work and this is the info box:

WIF keys are typed in Electrum, based on script type.

A few examples:
p2pkh:KxZcY47uGp9a...          -> 1DckmggQM...
p2wpkh-p2sh:KxZcY47uGp9a...    -> 3NhNeZQXF...
p2wpkh:KxZcY47uGp9a...         -> bc1q3fjfk...

I believe my key must be p2pkh but typing in "p2pkh:InsertMyKeyHere" does not work.
In this format  p2pkh: X -> Y. Is Y an output or are they both inputs?

I have been unable to type anything into the box which "un-greys" the "Next" box.

Any help working out the process from here would be greatly appreciated.

Cheers

[Charles-Tim]

WIF keys are typed in Electrum, based on script type.

A few examples:
p2pkh:KxZcY47uGp9a...          -> 1DckmggQM...

I believe my key must be p2pkh but typing in "p2pkh:InsertMyKeyHere" does not work.
In this format  p2pkh: X -> Y. Is Y an output or are they both inputs?

If the private key is correct, you should be able to click on 'next' which will result to the wallet sychronizing with the blockchain and show you if the address is funded or not by checking the balance. If it did not work and 'next' is not clickable, that means that is not a correct/valid private key. Also know that the WIF start form K, L or 5.

[Abedabed]

Ok that's a shame. Thanks heaps for the response 

[Charles-Tim]

I found a key which begins with a 1 on my old computer (2013) in a text document  and I have been unable to work out the process from

Also know that keys do not begin with 1, Bitcoin addresses begins with 1, 3 or bc1

Address that start from 1 are legacy addresses
Address that start from 3 are nested segwit addresses (also multisig addresses starts from 3)
Address that start from bc1 are native segwit addresses

If this is what you saw, they are addresses, you can also import it on electrum wallet but just to track the address transaction history and nothing more, you will need its private key to spend. If the address is valid also, you should be able to import it.

[nc50lc]

I found a key which begins with a 1 on my old computer (2013) in a text document  and I have been unable to work out the process from here to get to the bitcoin if it exists.

How many characters is that presumed private key?

As said above, "Wallet Import Format" (WIF) Private keys which what Electrum supports doesn't start with '1'.
It could be a ECDSA Private key depending on the number of characters, that only requires some formatting.
But do not share it to anyone including me.

[pooya87]

You can also check out this topic by @LoyceV which has a bunch of example private keys with different encodings/formats to give you an idea of what a bitcoin private key should look like (the type of characters, lengths, starting character, etc.).
What you have is most probably a legacy (P2PKH) address not a private key.

[LoyceV]

I found a key which begins with a 1
~
typing in "p2pkh:InsertMyKeyHere" does not work.

Omit the "p2pkh:" and enter only the address to create a watch-only wallet:

If there's a balance, you can continue your search for the actual private key.