[SOLVED] seagate external hard drive not recognized OS X

[tjknascar]

I can not add things or take things off my Seagate External hard drive. I have a Mac book Pro
OS X Yosemite
Help????

 

[kenrivers]

Is this a new drive or one that you have been able to use in the past? If it is new, did you format the drive before you tried to use it?