Not valid collateral. Anyone who supplies this loan will get negative feedback because it's frowned upon to sell accounts therefore your account is literally worthless.
If you can't sign a message then this account could of been sold a few months ago too. Follow the guide in the newbie sub forum it's simple to sign an address
You should read before spouting rubbish; The address cannot be signed, I can sign messages from old wallets or addresses, but for now the new blockchain.info addresses cannot do that. Don't take my word for it, ask around.
If you need to sign a message, export the private key and import it into electrum and then sign (keep the wallet passworded).
Second the post about accounts anyhow, try and find a different collateral.
Exporting to electrum makes no difference. You can only sign imported addresses from the old legacy wallet. As to what constitutes a valid collateral, It is up to the lender.