As you can see the partition 25gb is greyed out and the - minus sign isn't available I actually had this issue 2 months ago but i didn't find any solution now again I started searching for solutions and still no help Also, I has yosemite installed on it previously. I deleted it and I cannot delete the partition anymore.... I tried installing yosemite on it again...and guess what? It stops in between giving some error, when installing on that 25gb drive. Please help, I'm in desperate need. Thank you.