Blocked someone in Error.

I was on here earlier and was responding to a message from a member (we are not friends however). My laptop crashed and it took me sometime to get it working again. When I checked my messages all our earlier messages have disappeared. he has also disappeared from the list of members who viewed me. I think that I may have blocked him by accident. Can anybody help me to restore him so that we can message each other again and retrieve our earlier messages? Thanks