Thanks for your reply. I used Multibit at the time and never bothered to use a passphrase or password. It was such a small amount and I only sent a small amount to a friend just for fun to see how long it took to arrive. I soon lost interest and forgot all about it. At the time it was worth 10 dollars or less but a lot has changed since then. I just counted the characters of the key and it has 51 characters so I'm sure it is the private key.
I understand Multibit is not even used anymore. What program could I use to enter the keys in?