Oh I got my private key from Bitpay but Electrum wont accept it. I will try your method above though - tried it, it asked for my phrase which I provided and it kicked out the same private key I already have and electrum still will not accept it. So, is my account hinged on the single aspect of signing a transaction?? I understand the usefulness of this aspect but my current wallet does not allow for signing and my knowledge about importing private keys to another wallet is obviously lacking.
You can follow this
instruction on how to import private keys to electrum, please use the latest version of
electrum 3.3.7 for your safety.
As long that you succesfully imported the private key, you can sign message with the address assigned on the private key.