Disk error
Hello,
I have an error with a disk; it is unmountable. I do not really care about the data, but whenever I try to mount it via Disk Utility it says I should go to first aid and Repair the disk. The button "Repair Disk" is grayed out, so I cannot press it. I have tried verifying it, but it says "Error: This disk needs to be repaired. Click Repair Disk." How can I repair/restore/reformat it so I can use it again?
Thanks for your help.
Mac mini, OS X Mountain Lion (10.8.3)