Remove duplicates

I need a way to do a conditional check for duplicats. I have a sheet that has alot of members in it in the format of Last,First,Middle. What I need is that when I enter another person into the sheet it need to check for a duplicate however the problem is if I just have the Last,First name it wont find the duplicate. We tried it with the conditional formatting to turn the cells to red when found but that wont work either. ANY IDEAS??

Thank You so much

Randal