Problem with mail merge in Outlook

Hello all, I'm having a problem using mail merge with Outlook. We usually send out a mass email once or twice a month, and have had no problems with it, up until a few days ago. The problem being that the option to mail merge has just disappeared from the tools tab, nor am I able to find it in the customize tab either. I'm fairly useless with outlook as it is, and am even worse when stuff goes wrong in short, help!