PLEASE ACCEPT MY APOLOGIES i AM NEW HERE AND i NEED HELP i DON'T FIND THE COMMAND TO START A MESSAGE.

I have Outlook 2010 I have been using for long time. However, yesterday after I sent a message to my contacts groups STUDENTS NOW THE CONTACT DISAPPEARED . i need to get it back it has almost 300 addresses It i will take a long time to type one by one. When I click it to open it it is empty. please help