There are several questions here:
1. What was the original software that generated the key?
2. Is it a private key in the first place or a seed?
3. What happened with the original wallet you used that key with where you received your coins? Why don't you send the coins from there to a different wallet?
4. If this is in fact a seed and you imported it into Electrum, did you tick the option "BIP39 seed" and selected the correct derivation path that corresponds with your address format?