No inputs sounds like there are no bitcoin to sweep. Do you maybe want to import a key? If so you need to restore a wallet and use the private key as seed in order to import it without sweeping.
I don't know how that would be possible. I did load it once and it did nothing...But that was with another key and it never showed any balance.
How do I go about it your way?
Is the key encrypted? Does it start with 5,L or K? If it doesn't you probably have the wrong key and you have to either decrypt it on bitaddress.org in the wallet details tab.
To import a wallet, go to File>New/Restore, type any name or leave it as it is. Next, go to Restore a wallet/Import keys, press the standard wallet and type the private key into the box. Click next, and type any password if you want. You should have the key imported into the new Electrum wallet that you have created. To go back to the old one, simply go to File> Recently Open and select your another wallet.