Would you mind to check or giving a few samples of what the secretkey looks like? Like I said in my previous post if the first character starts with K or L that is a WIF key you can able to import it to any wallet that supports a WIF key like Electrum you can follow the guide that I posted above.
If the first character is different then that's not a WIF key if that's the case you might need to read the list of address prefixes to recognize what's in the secretkey once you found out update here.
Here's the sample of the content of old wallet.dat before just found it on pastebin but it is only secret and it is decoded into hex if yours looks the same as this then you might need to convert it into a WIF key the only working tool that you can convert the secret is by using the bitaddress tool but it's not safe to use online you need to run it into an offline device for safety purposes.
addr = '1AJ3vE2NNYW2Jzv3fLwyjKF1LYbZ65Ez64'
sec = '5JMhGPWc3pkdgPd9jqVZkRtEp3QB3Ze8ihv62TmmvzABmkNzBHw'
secret = '47510706d76bc74a5d57bdcffc68c9bbbc2d496bef87c91de7f616129ac62b5f'.decode('hex')
pubkey = '046211d9b7836892c8eef49c4d0cad7797815eff95108e1d30745c03577596c9c00d2cb1ab27c7f95c28771278f89b7ff40da49fe9b4ee834a3f6a88324db837d8'.decode('hex')
ckey = '0f8c75e4c6ab3c642dd06786af80ca3a93e391637d029f1da919dad77d3c8e477efd479814ddf4c459aeba042420868f'.decode('hex')
In case the secret is the same as this in hex format and want to convert it then here's the link below
- https://github.com/pointbiz/bitaddress.org